Diavolo/Personality and Relationships

Personality
"This is a test... a test from the past that I must overcome."

- Diavolo, to Polnareff

Diavolo is an extremely prideful mob boss, ruthless and brutal in his will to hide his past and maintain his position at the top of his gang Passione. Diavolo shares his body with an alternate personality dubbed Doppio.

The biggest personality trait Diavolo shows is his obsession with erasing any trace of his past and hiding himself from the world, a compulsion he tries to fulfill by any means. He is insanely 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 hotel rooms exclusively.

The mob boss has a violent tendency to hunt and kill those who try to uncover his past, 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 in JoJo's Bizarre Adventure share a mystic spiritual link, being able to sense each others. 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 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 Sorbet and Gelato, who Diavolo had killed and in the case of Sorbet, cut in piece and framed in glass, delivered to La Squadra di Esecuzione as a grim warning of the fate awaiting traitors. Diavolo is also persistent in keeping himself a secret even from Doppio, his most trusted subordinate and alter-ego, despite the fact that several people thinking that if he and Doppio worked together with equal knowledge they could be unstoppable.

Diavolo's 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 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, 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 forever. This disproportionate pride is backed by the firm belief that he's blessed by Fate, as Diavolo's past involve extremely unusual circumstances such as an unaturally 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 powerful Stand. Diavolo considers himself extremely lucky as well. Diavolo readily accepts any difficulty as a "test" he'll have to overcome to prove himself, 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's death and had no idea of his new powers. Against Requiem Diavolo's confidence crumbled when it countered his time erasure ability and made 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 has him frightened being approached by a little girl, his pride and confidence completely crushed.

Diavolo has also demonstrated an inability to understand other people's emotions and to properly interact with anyone, due in no small part to his overwhelming pride and secretiveness. For instance when Bucciarati revolts, Diavolo thinks that Bucciarati merely wants to overthrow him, without considering that hurting his own daughter deeply angered Bruno. Also forgetting that La Squadra di Esecuzion 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. However, Diavolo is also domineering and aggressive, taking his thoughts for absolute truths and ordering his interlocutor around; When he is angry, Diavolo is prone to shout insults and issue death threats. Diavolo only commands the respect of his subordinates through greed or fear, causing Passione to 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, especially traitors. Should anyone try to approach his alter ego Doppio and pry too much on his past, Diavolo violently rebukes them. For instance Diavolo nearly gouged the eye out of the taxi driver that robbed Doppio and harassed him.

Diavolo approaches fights coldly, only considering them as chores to be completed to maintain his supremacy. Diavolo favors finishing off his victims quickly using his King Crimson to confuse them and kill them in one move. As seen with Bruno, Diavolo is slightly amused (at least his Stand is) by the futile efforts of his opponents, and boasts regularly about his 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.

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 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 village to the ground 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

 * 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 Silver 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 who he leave 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.
 * Donatella Una: 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 existance until Donatella passed away and La Squadra begun looking for clues on their former employer's identity. Diavolo realizes that their bond of blood allows him to sense her presence(Since bonds of family are almost a supernatural force in the world of Jojo)  Immediately realizing that she could sense him as well, he put up a plan to kill her and used Bucciarati's group as pawns to do so. In the final battle, Diavolo disowns Trish, wishing she never had been born. When she foiled her plan one last time, Diavolo snapped and punched through her stomach although she survived.

Enemies

 * Giorno Giovanna: Giorno planned to take down Diavolo since the beginning due to his plans to distribute drugs, which were reaching children. Because of this, Diavolo retaliated and made Giorno his enemy. The two became bitter enemies at the end of Part V.
 * Bruno Bucciarati: Prior to meeting Giorno, Bucciarati was loyal to Diavolo, even though he was aware of how evil the boss could be. With urging from Giorno, Bucciarati became determined to take the boss down as well, eventually dying because of it. Diavolo respects Bucciarati to a degree, complimentating him on his prowess and valor.
 * Narancia Ghirga: Although not directly interacting with Narancia, he was Diavolo's first victim after Silver Chariot Requiem activated and Doppio was shot by Mista.
 * Leone Abbacchio: Diavolo feared Abbacchio as, due to his powers, he could easily find out who their Boss was. As such, when given the change, Diavolo assassinated Leone while posing not only as Doppio, but also as a simple kid playing soccer.
 * 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. However he chose to remain on Diavolo's side. In a rejected storyline Fugo was also sent to kill his former friends. If the story line was kept, Araki admits that Giorno would have needed to give the killing blow, which Araki felt would be too heartbreaking. However, in the light novel, Purple Haze Feedback, Fugo swears loyalty to Giorno.
 * Guido Mista: While Diavolo lacks a connection with Mista, Mista on the other hand shares his teammates hatred and fear of the boss.
 * La Squadra di Esecuzion: To say La Squadra hated Diavolo is an understatement, seeing how he not only refused to give them a territory, but also chopped one of their members up into 36 individual pieces and then mailed each piece individually back to them.  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 disdain these assassins, but came to respect 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.
 * Cioccolata and Secco: As immoral Diavolo was, he considered both of them complete monsters and only kept them in his organization due to their powerful combination. On their part, Cioccolata and Secco only obeyed Diavolo because he let them torture people and planned to overthrow him eventually.