Diabolik is a ruthless master thief. He typically steals from criminals (and has no issue with killing them if need be, but rarely, if ever, kills the innocent or the police), and has a set of lifelike masks which he uses to fool his opponents, assuming every identity at his will. He seems to have a deep knowledge in many scientific fields, including chemistry, mechanics and computers. In his first appearances, Diabolik was a more straightforward villain who did not hesitate to murder anyone in order to accomplish his deeds. He was later given a more "Robin Hood"-like persona and was shown stealing essentially from criminals, in order to soften the series’ violence and amorality.
He was raised as an orphan on a secret island hideout of a criminal combine, where he learned all his criminal skills, including developing his special masks, before killing the head of the combine. Diabolik’s true name had never been revealed in the series, and he doesn’t know it himself. Diabolik took his name from a dangerous black panther that the head of the combine killed on the secret island. From issue #3 of the series, Diabolik is aided by his "moll", Eva Kant, who has gained an increasing role as his partner and lover.
Diabolik always drives a black 1961 Jaguar E-type. Graphically inspired by the actor Robert Taylor, he usually wears a skintight black body suit that leaves only his eyes and eyebrows (very distinctive ones) exposed when going "into action". Diabolik does not use firearms: his main weapons are the daggers he throws with uncanny ability, as well as a small dart gun with knockout darts. Eva drives a white Jaguar, and unusually goes into action wearing a heavy sweater and pants, no mask and no revealing clothing. The stories are set in a fictional town, Clerville, loosely inspired by Geneva, Switzerland.
Diabolik’s main opponent is Inspector Ginko, known only by his surname, a fierce and incorruptible police officer who is almost always thwarted by astute tricks devised by Diabolik. The only other recurring character is the noblewoman Altea, Ginko’s fiancee.