Diavolo/Personality and Relationships

Personality
"In order to grow, we must defeat the mistakes of our past. The past... even when you break it to pieces and entomb it in stone, it crawls out like a worm."

- Diavolo

The biggest personality trait Diavolo shows is his obsession with erasing any trace of his history and keeping his presence a secret from the world, a compulsion he tries to fulfill by any means. As he believes the mistakes of the past or simply the past itself is something to be defeated and destroyed in order for human beings to grow, he is exceptionally anxious about his past, linking it to fear, and being apprehensive of anyone learning of him. Even in the already secretive Passione hierarchy, Diavolo goes to excessive length to hide his identity and his face, issuing orders through several proxies or by computer so that nobody ever meets him personally. Diavolo lives most of his life in the shadows, hinted to perpetually travel across Italy hidden in Doppio, his alternate personality, and sleep in motel and hotel rooms exclusively. This compulsive trait of erasing his past is also an allegory to the inherent imperfection in King Crimson, specifically Epitaph's ability; While he can see into the future so as to avoid any mistakes, Diavolo's Stand ability cannot erase any low points or 'ebbs' in his life that have already occurred, forcing him to try to fix his errors through his own personal, manual efforts.

Diavolo has a violent tendency to hunt and kill those who try to uncover any kind of personal information, or are merely susceptible to lead his enemies to him, as shown by his will to kill even his own family if it means keeping his identity safe - something highly vocalized through his attempts to murder his daughter, whom has never even met Diavolo herself and only knew things her mother passed down. This is however partially justified since family members within the JoJo's Bizarre Adventure universe share a mystic spiritual link, with Diavolo and Trish being able to sense each others' souls and know where the other is as well as if they are alive. Nevertheless, Diavolo is sufficiently pragmatic not to go on a killing spree every time he's about to be discovered, notably only using his power to confuse a hotel cleaning maid just for as long as he needs to erase any trace of his presence. As soon as he learns of a Passione member trying to investigate him, they will be dubbed as traitors and made examples of his wrath and absolute power. Most notable are, whom Diavolo had killed and in the case of Sorbet particularly, cut into pieces and framed in formalin, then delivered to Squadra Esecuzioni as a grim warning of the fate awaiting potential traitors. Diavolo is also persistent in keeping himself a secret even from Doppio, his most trusted subordinate and alter-ego.

His second most prominent personality trait is his pride and confidence, firstly in his nigh-invincible Stand King Crimson, then in himself. Operating under a philosophy that King Crimson makes him invincible because it allows him to see the "pitfalls" in the future and avoid them, and allows him to manipulate Fate and reality by choosing to nullify arbitrarily chosen events, he justifiably boasts about King Crimson's power regularly. Diavolo notably claims that anyone's actions before King Crimson are vain, which is true to a degree. Secondly, Diavolo is intimately convinced of his innate superiority over humanity. Using epithets such as "Emperor" or "King of Kings", or like other main antagonists in the series, and using the prefix I or Me (この,  kono?) to announce his name in a sign of superiority over others. The mob boss doesn't doubt that he is fated to remain at the top, or 'apex' as he describes it, forever. This disproportionate pride is not only derived from his idea that people grow from defeating their past (and therefore, he has grown much due to his constant attempts at erasing any type of history of his), it is also backed by the firm belief that he's blessed by Fate; Diavolo's past involved extremely unusual circumstances such as an unnaturally long pregnancy in an all-female prison, making his birth nothing short of a miracle, then him finding six Arrows which would grant him his extraordinarily powerful Stand as well as his massive wealth.

Other than his own philosophy of defeating the past so as to mature, Diavolo also lives by another thematic philosophy that results are the only things that matter in the world. As a decisive and assertive crime boss, Diavolo doesn't hesitate to take shortcuts or directly involve himself with troublesome matters if those actions are the quickest and easiest paths to an end. King Crimson's ability is an echo of this, and maybe the source of it, leaving nothing but the outcomes of situations, specifically those he himself sees fit to keep. He abuses his Stand's power as a means to produce the most favorable conclusions to his problems, and at the same time boldly prove his philosophy's claim to anyone that he confronts. Diavolo shows a degree of prioritization for these results and answers as well, notably when he, upon meeting with Polnareff whom he thought he killed years ago, only questions him as to why he would have an Arrow before attacking once more, rather than how he learned the name of the boss of Passione, or even how he managed to survive being thrown off a cliff into rocky waters.

For Diavolo, keeping stability within Passione is secondary to maintaining power and his status as the boss; a mentality that eventually realizes the corruption of Naples, worsens the city's drug problem, and ultimately, leads to the rousal of Giorno Giovanna into joining the gang seeking to dethrone their boss. Diavolo only commands the obedience of his subordinates through greed or fear, causing the organization to even be corrupted within itself, members turning against each other, and multiple people to plot against him. Diavolo is also unforgiving of those he considers enemies, most especially traitors. Should anyone try to approach his alter ego Doppio and pry too much on his past, Diavolo violently rebukes them. For instance, he nearly gouged the eye out of the taxi driver that robbed Doppio and harassed him, and outright and violently murdered a fortune teller that correctly divined his history.

As an extension of the idea that he is blessed by Fate, Diavolo considers himself extremely lucky as well. He readily accepts any difficulty as a "test" he'll have to overcome to prove himself as standing above everyone, and though he can be subject to anxiousness or despair, his pride will prevail and he will constantly choose to confront directly whatever problem he has. This causes him to foolishly face Gold Experience Requiem head-on, although he did foresee Giorno Giovanna's death and had no idea of his new powers. Against Requiem Diavolo's confidence crumbled when it countered his time erasure and prediction abilities and left him powerless. When he found himself trapped in an endless death loop, unable to do anything about his situation, Diavolo panicked and his last appearance in the story has him frightened being approached by a little girl; His pride, confidence, and to varying degrees, sanity being completely crushed by his everlasting fatalities.

Diavolo has also demonstrated an inability to empathize or even understand other people's emotions and morals, especially those righteous, as well as an inability to properly interact with anyone, due in no small part to his overwhelming pride and antisocial secretiveness. When Bucciarati revolts, Diavolo openly theorizes that Bucciarati merely wanted to overthrow him or was opportunistic in his presence, without considering that hurting his own daughter deeply angered Bucciarati. Also forgetting that Squadra Esecuzioni would have a grudge against Diavolo after killing Sorbet and Gelato, he sent them to investigate Donatella's house, allowing them to uncover the existence of Trish. When interacting with others, Diavolo tends to act rather respectfully for his opponents and subordinates if they are obedient and competent. He compliments both Risotto and Bucciarati for their resourcefulness during their battles, and offers Risotto an honorable death. On a smaller scale, he compliments a fortune teller capable of accurately deriving his past as being "the best of the best" and gave a brutal yet painless death. However, Diavolo is also domineering and aggressive, taking his thoughts for absolute truths and ordering his interlocutor around; When he is angry, he is prone to shout insults and issue death threats.

Diavolo approaches fights coldly, only considering confrontations as chores to be completed to maintain his supremacy. Diavolo favors eliminating his victims quickly using his King Crimson to confuse them and kill them in a single move. As seen with Bucciarati, Diavolo is shown slightly amused (or at least his Stand is) by the futile efforts of his opponents, and boasts regularly about his perceived invincibility. A pragmatic man, Diavolo still approaches the situation carefully, especially when Doppio is in command, and cannot use his full power. In an unadvantageous situation, Diavolo is patient, carefully undermining the enemy before using one critical attack, making him a most dangerous enemy during any battle, regardless of King Crimson's time erasure.

During his youth, the teenager named Diavolo was described as dim and timid, but well-meaning. He also expressed his wish to become a sailor and had a girlfriend Donatella, they were sufficiently close enough to have a child together. Due to the lack of further information and Diavolo's alternate personality disorder, it is unknown if this was a facade, or if he was genuinely like this before. Either way his secretiveness and ruthlessness were already present, having hidden his mother underground and having burnt his home village to the ground simply to hide his past.

For unknown reasons, Diavolo kept his mother alive, albeit trapped underground, and his old girlfriend Donatella alive, despite his willingness to kill his daughter.

Relationships
"You are the very definition of nauseating evil! You abuse the innocent and unknowing! All for your own personal benefit!"

- Bucciarati to Diavolo


 * With Alter Ego:
 * Diavolo to Doppio: Although in most cases it's self-preservation and survival (assuming killing Doppio would kill Diavolo, or vice versa), Diavolo seems to have a lot of affection for Doppio: he put Doppio in a very dangerous position of being the underboss instead of a usual subordinate, he often gave Doppio directions to being successful and even warned him to keep away from Nero and encouraged him to flee, and most peculiar of all, he has a habit of sometimes calling Doppio "[his] (cute) Doppio" with the more down-to-earth "watashi wa" pronoun.  Noticeably, when Chariot Requiem activates and Doppio is shot multiple times by Mista, Diavolo almost immediately destroys and impales Narancia on a gate, instantly killing him, and begins to attempt more murders - before it happened, Diavolo was perfectly hidden away and everyone assumed Diavolo was in Bucciarati's body. On the other hand, Diavolo doesn't spend a single thought for Doppio whom he left for dead in Bucciarati's body.
 * Doppio to Diavolo: While Doppio never learned the truth between themselves, he highly respects Diavolo and always called him "Boss" - though, whether or not Doppio knew Diavolo's name is unknown. Doppio also seems to be Diavolo's gopher, something he takes pride in considering how loyal he was to a point of stubbornness, and he seemed heed most of Diavolo's orders when he remembered them. According to Doppio himself before his death, Diavolo had told him that staying in Bucciarati's body would be dangerous and decided to move, leaving Doppio to his fate.
 * Although it's unknown how their relationship went, outside of Diavolo refusing to give her a name and never talking about himself, it can be inferred that it was largely positive. He took a picture of Donatella and she kept it throughout the years (although Diavolo becomes enraged upon learning that it still exists). Interestingly enough, Diavolo also never attempted on Donatella's life despite his ruthlessness. Likewise, Donatella loved Diavolo and told her daughter good things about him (albeit all lies Diavolo said before hand), and it's known that as Donatella died from her illness, she wished to see her lover again.
 * Trish Una: It's inferred that Diavolo was never actually aware of Trish's existence until Donatella passed away and Squadra Esecuzioni begun looking for clues on their former employer's identity. Diavolo realizes that their bond of blood allows him to sense her presence (the bonds of family being a reoccurring supernatural force in the world of JoJo). Immediately realizing that she could sense him as well and jeopardize his anonymity, he set in motion a plan to kill her with his own hands and used Bucciarati's group as pawns to bring her to him without letting the traitors capture her. In the final battle, Diavolo disowns Trish, wishing she never had been born. When she stops him from getting the Arrow during the final battle, he responds by having King Crimson punch clean through her stomach in a final attempt to kill her. However, she would survive due to Bucciarati's interception. Afterward, Diavolo would at the very least thank Trish for giving him the courage to attack Giorno Giovanna, as she revealed to her allies that Diavolo was attempting to run away, tempering his pride.

Team Bucciarati

 * Giorno Giovanna: Giorno planned to take down Diavolo since the beginning due to Passione's corruption of Naples, which included an agenda of drug trafficking affecting even children. Because of this, Diavolo retaliated and made Giorno a high-priority target. The two became bitter enemies over the course of Part 5, with Diavolo having invoked Giorno's anger during their confrontation after the death of Narancia, and Giorno helping to rouse Team Bucciarati's betrayal. During the race for the Arrow, Giorno alone figured out that Diavolo was residing in one of the group's bodies, causing the Boss to realize that Giorno was his greatest threat. With Bucciarati's demise, Diavolo confirms that Giorno was in fact the more dangerous individual due to his cunning, as well as the fact that he had planned to usurp him the moment the boy entered Passione.
 * Bruno Bucciarati: Prior to meeting Giorno, Bucciarati was loyal to Diavolo, even though he was aware of the gang's involvement in the drug trafficking within Naples. Although Bucciarati initially had no power to take action, with urging from Giorno, he became determined to take the boss down as well. While this eventually led to Diavolo's killing him, Diavolo had declared his respect for Bucciarati, complimenting him on his prowess and valor.
 * Narancia Ghirga: Although not directly interacting with Narancia, he was a threat nonetheless once he turned traitor. After Chariot Requiem was activated and Doppio was shot by Mista, Diavolo retaliates by killing Narancia, whom had a radar capable of finding anyone attempting to attack Chariot Requiem.
 * Leone Abbacchio: Diavolo feared Abbacchio as he could easily find out whom Passione's Boss was with his powers. As such, Diavolo personally went back to Sardinia to intercept Abbacchio, and when given the opportunity, assassinated him while posing not only as Doppio, but also as a simple child playing soccer.
 * Guido Mista: While Diavolo lacks a connection with Mista, Mista on the other hand shares his teammates hatred and fear of the boss. Diavolo likewise regarded him as a threat just for betrayal. In the end, after the final battle with Diavolo, Mista was the last original member of Bucciarati's team before Giorno intact.
 * Pannacotta Fugo: Fugo, even with all the evidence given to him, was torn between swearing loyalty to Bucciarati or staying on Diavolo's good side. Understanding the extreme danger of betraying Passione and Diavolo, Fugo ultimately chose to remain on Diavolo's side. In a rejected story line, Fugo was also sent to kill his former friends, and if that was kept, Araki admits that Giorno would have needed to give the killing blow, which he felt would be too heartbreaking.
 * Jean Pierre Polnareff: Polnareff is one of Diavolo's many enemies, though Diavolo did not have any interest in Polnareff particularly. As soon as Diavolo found out Polnareff had been investigating him, he made a personal and brutal attempt to dispose of him, but unknowingly left him alive. During their second confrontation, Diavolo did not care much that Polnareff was still alive, nor that he knew his name, but rather wanted to know immediately why Polnareff would possess an Arrow, displaying a sense of urgency on the matter of his familiar foe. Nonetheless, Diavolo would, without much effort, successfully put an end to Polnareff once more, stepping on his neck in order to check his pulse and confirm his death. However, Diavolo did not know that Chariot Requiem would save its former master by preserving his soul in the body of the turtle Coco Jumbo.

Other

 * Squadra Esecuzioni: Diavolo not only refused to give La Squadra a territory and higher pay, but when the first signs of betrayal started showing, also killed, one of whom was sectioned into 36 individual pieces, which were then mailed individually back to the group. It should be noted that it took La Squadra two years to form a retaliation plan, which Diavolo immediately found out about and retaliated against. Diavolo disdained these assassins, but came to respect their leader, Risotto Nero to a degree, considering him a worthy opponent and granting him the dubious "honor" of a painless death if he obeyed his command of restoring his iron level during their fight.
 * Cioccolata and Secco: As immoral Diavolo was, he considered both of them complete monsters and only kept them in his organization as part of his personal guard squad due to their powerful combination and individual abilities alike. On their part, Cioccolata and Secco only obeyed Diavolo because he let them torture people and planned to overthrow him eventually.