Denji's Father

This unnamed man was the father of Denji. When Denji was young he killed his father in self defense, as his father was in a drunken aggressive state and he feared for his life. His fathers murder was ruled a suicide by the adults in Denji’s life as acknowledging his death as a murder would mean they would be unable to get any money from his death. After his death, Denji inherits his debt to the Yakuza.

Appearance
Of the little that is seen of him, Denji's father seemed to have the same hair just as his son.

Personality
Little is known of his personality, as he was deceased prior to the chronological beginning of the plot. Makima describes him as an abusive alcoholic, who was violent enough with Denji to the point where he was killed by his own son in self-defense. It is also implied that he had an addictive personality, losing large amounts of money to the Yakuza resulting in a massive debt which Denji later inherited.

Control Devil arc
Makima, when revealing her intentions to Denji, reveals that she investigated his past and knows that his father died not from suicide, but rather from being killed at Denji's hands in an act of self-defense. His supposed suicide was, in reality, a ruse created by the Yakuza in order to have Denji inherit his debts.

Denji had been repressing this fact behind a psychological barrier, which is represented by an closed door, and when the memory comes to light Denji sees himself as a child, standing over his father's wounded and bleeding corpse.