Main character of the saga and thief, Diabolik works almost every time wearing black tights that cover his whole body but his grey eyes that are cold like steel. He mainly steals really precious jewels or huge amounts of money and he does not hesitate to kill who gets in his way. Even if what he does is illegal, Diabolik has high and deep-rooted personal principles (honor, protection of weaker people, friendship and gratitude, respect for great-heartedness) so he hates people who deal with Mafia, drug-dealers, loan-sharks and torturers. In the "cult" issue called "DIABOLIK, WHO ARE YOU?" (1968) we get to know that our protagonist is the only survivor of a ship-wreck and that he was saved, while he was a babe in arms, by King, the head of a powerful criminal organization that has its headquarters on an island far away from every known route.

Diabolik grows among all kinds of criminals, without being left in anyone's care, but getting "pieces of information" from the various experts who work with King. Thanks to the teachings of Dr. Wolf, the head of the chemical laboratory, Diabolik creates the first of his famous masks that allows him to replace anyone's identity.

By replacing King's identity, Diabolik was able to steal from him and kill him, before leaving the island in order to begin his new and unstoppable criminal activities. Diabolik will choose his name by himself, inspired by the name of a lethal panther that was killed and stuffed by King. We lately got to know that after his escape from the island and before his arrival in Clerville, Diabolik passed a lapse of time in the East, in order to refine some of his techniques. Even if the State of Clerville abolished the death penalty, Diabolik will be immediately sentenced to death by decapitation if arrested.