Diavolo is a tall man with a lean and semi-muscular build. He has long hair, leopard-patterned with various spots, parted in a zig-zagging manner; the bangs of which are propped and parted slightly to the side. The rest of his hair is cut straight across at his shoulders. His shirt, hidden under Doppio's sweater, appears to be made of complex mesh-wiring: it covers his shoulders and torso but down his back and abdomen are linked circles that are tucked under his belt, which in the back end in two~three long "coat tails". On his arms are elegantly designed floral sleeves leading down to a pair of wristbands. He also shares a pair of studded pants and seemingly sock-less loafers with Doppio.
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.
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 Sorbet and Gelato, 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.
Diavolo's Stand is King Crimson, an extremely powerful Stand with tremendous physical strength and the ability to erase time up to a 10 seconds time frame as well as predict anything that happens over the following 10 seconds. Although it has some limitations, King Crimson renders him essentially invincible in a fight as he can either foresee and counter the enemy's actions or render them meaningless by erasing the timeframe in which they happen.