Diavolo

Diavolo is a veritably tall man in his 30s with a lean and semi-muscular build. In his first appearance, covered in shadow in all but his glaring eyes, he appears to have short, combed back straight hair and is wearing a suit and tie.↗

His appearance is drastically altered when fully revealed: Diavolo has long hair, dyed with various spots in a leopard pattern and parted in a zig-zagging manner. His bangs are propped and parted slightly to the side, and the rest of his hair is cut straight across his shoulders. In earlier depictions, varying amounts of Diavolo's hair were cut straight, inconsistently ranging from small locks to the entirety of his hair. 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 or three long "coat tails".↗↗

The biggest personality trait Diavolo shows is his obsession with secrecy; emphasizing the erasure of any trace of his history and keeping his identity a secret to assume his position of power as a compulsion he will fulfill by any means necessary. As he believes the mistakes of the past, or simply the past itself, are something to be defeated and destroyed for human beings to grow, he is driven anxiously about his past being a threat to him, linking it to fear, and being exceptionally apprehensive of anyone learning of him.↗

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 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.↗

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. That being said, 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.↗↗

Stand

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.↗

Double Personality

Diavolo and Doppio are two souls that inhabit the same body. As a result, they can switch their personalities as well as their physical appearance. Compared to Diavolo, Doppio appears a lot younger and is described by a fortuneteller as looking too young to have children. Diavolo appears to be a lot taller, as well as more muscular. When he takes over, Doppio's freckles disappear, his voice deepens, and his hair is seemingly a different length. According to Diavolo, it takes a couple of seconds for him to completely take over Doppio's body.↗↗↗↗

While Doppio is in control, Diavolo recognizes things that Doppio doesn't. For instance, he was able to tell that the taxi driver didn't see the picture of Donatella that Doppio was carrying, despite his subordinate's beliefs, and was later able to see the lurking Risotto.↗

Soul Manipulation

Diavolo is exceptionally knowledgeable about souls and their mechanisms, and is also equally skilled at manipulating his own soul.↗

Spiritual Connection

As Trish Una 's father, Diavolo has a spiritual connection to her. By instinct, he can sense that she is indeed his daughter and was able to feel that she was alive despite being informed that the plane she was on had crashed.↗

Intelligence

Diavolo is a gifted tactician and is generally more intelligent than average. As proof of Diavolo's abilities, the Boss has built a powerful gang with influence spreading across Italy in a matter of years.↗

Personal

Though never demonstrated, Diavolo can fluently speak Sardinian.↗↗

Chapter 443: Bucciarati is Coming, Part 1 (Mentioned) Mentioned only↗

Chapter 444: Bucciarati is Coming, Part 2 (Mentioned) Mentioned only↗

Chapter 446: Bucciarati is Coming, Part 4 (Mentioned) Mentioned only↗

Chapter 447: Bucciarati is Coming, Part 5 (Mentioned) Mentioned only↗

Chapter 448: Meet the Gangster Behind the Wall, Part 1 (Mentioned) Mentioned only↗

Hirohiko Araki stated that he could have created a villain that was similar to DIO to appeal to popularity, but preferred adding variety rather than rehash previous characters. With that in mind, he designed Diavolo to be a different kind of evil, one just as powerful and captivating as DIO or Yoshikage Kira, but with a distinct identity. Despite being a mafia boss, since one of the themes of Part 5 was to "draw bishonen characters," Araki decided not to design Diavolo as an older, imposing figure like Marlon Brando 's character, Vito Corleone, from The Godfather.↗↗

Casting

Kellen Goff, Diavolo's voice actor in the English dub of the anime, additionally auditioned for Vinegar Doppio as well as Diavolo, though he only won Diavolo's role. He theorizes that Diavolo's personality contains a bit of Doppio's personality in it that resurfaces when Diavolo loses his cool, and compares Diavolo to a child who is "playing the boss". This influenced his performance, and every time Diavolo loses his calm, Goff voices him with a higher pitch to evoke the idea that Diavolo's childish side resurfaces.↗↗↗

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 a more down-to-earth "watashi" (わたし) pronoun.↗

Family

Donatella Una: Although the specifics of their relationship are unknown, outside of Diavolo never talking about himself and going by the false name of "Solid Naso," it can be inferred that it was largely positive on both sides. Diavolo took a picture of Donatella once, which she kept throughout the years (although he becomes enraged upon learning that it still exists). Interestingly enough, Diavolo never attempted to have Donatella executed despite his ruthlessness.↗

Mother: Diavolo's mother was incarcerated at the time of his birth, and remained so for the first eight years of his childhood. At some point, Diavolo met his mother and, for unknown reasons, sewed her mouth shut before binding and burying her beneath the floor of his room.↗

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. 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.↗

Other

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.↗