In his mortal form, Drip appeared as a sinewy, lightly built humanoid rat of average height, sometimes described as short, with blue fur, a white snout and distinctive black markings on his face.
As a Sin, he is approximately nine feet tall, and no longer humanoid, now more resembling an actual rat walking on its hind legs, with a distended abdomen and a grotesquely elongated lower jaw. His penis changes shape constantly.
Drip was a serial rapist and killer, mainly of young women, whom he hunted and murdered in the dozens, if not hundreds. In fact, nobody in his vicinity was safe. He was a wanted man for an unknown period of time, until finally either apprehended or killed.
After his death, he was sent to Hell where he was repeatedly gang-raped by women in hell, furthering his hatred of them. He was given the position of the embodiment of the deadly sin Lust. In this capacity, he serves to torment the denizens of Hell; he, himself cannot derive sensual pleasure from the torture he inflicts, unless the victim has willingly given itself over to him for some reason, usually a supernatural favor.
Drip is a merciless, vicious monster whose only goal in life appears to be spreading as much pain and misery as possible - and that's a lot. His previously keen intelligence was seemingly dulled by his life in Hell, and he has served as part of the other Sins' machinations.
Because Drip's parents died so soon after his birth that he has no conscious memories of them, he was raised by his grandmother. This woman displayed all the traits Drip would show off as an adult, only on a smaller scale. She psychologically, physically and sexually abused the still-innocent child, constantly imprinting on him the notions that he was worthless, that nobody could be trusted and that everyone could be manipulated through sex.
Although Drip was utterly in her power, in the end, he killed her, and she went to Hell, where she was immovably sealed in a wall of sin. Now reunited with her grandson, she still manages to exert power over him; he is still afraid of her, even now that he has god-like power, and still serves her depraved whims.
While even Drip might eventually seek redemption, the forces of Hell actively conspire to keep him from this. They managed to discourage any future attempt at being reborn by telling him that, in his next life, he would be a woman.
Although all Sins are Jack's enemy, Drip might be the one who hates him most, and whom he hates most - for good reason. After Jack came to the rescue of Arloest, a soul wrongly kept in hell by Drip after a bad deal, he swore revenge. To get at Jack, he harmed the one person Jack loved the most, Drip's own innocent son Fnar. After Drip most likely raped the boy, taking his innocence and opening his eyes to the suffering of his surroundings, Jack was shocked when his angelic friend Farrago revealed it was she who asked that Fnar remain with Jack in Hell so that he could help bring out the goodness in Jack. Enraged and overpowered by his own anger, he tried to choke the life out of Farrago before Fnar begged him to stop. Jack then left and battled Drip. With his new-found power, he removed his brother Sin's head and contained the rest of him inside his own self.
Jack was denied the right to say goodbye to Fnar before he was reborn, when the angel Central threatened to kill him should he go near either the boy or her young apprentice Farrago. They haven't spoken since, while Drip's head remains alive by Jack's own power, (so that he will not die and regenerate) keeping the being that is Drip sealed away within the sin of Wrath and his physical manifestation out of hell...for now.