Anthony Rizzoli was the son of Salvatore Rizzoli, the head of the Rizzoli crime family. Sometime before 1950, Anthony would succeed his father and eventually would go by the moniker of Underboss. 
Shortly after his father's death, the Rizzoli family became embroiled in a five-family gang war, from which they emerge victorious. Underboss incorporates two rival gangs into the Rizzoli hierarchy, greatly increasing his family's power. With Underboss in charge, the Rizzoli family's criminal empire would dominate organized crime throughout New York City for more than fifteen years.
In 1965, Underboss was captured by Nite Owl II and Rorschach in his hideout, located in sewer, during the height of his criminal empire and was put in Sing Sing. In 1973, however, he broke out of prison during a riot with the help from Jimmy the Gimmick, but was set up for the murder of Bob Woodward and Carl Bernstein.. The whole Underboss escape turned out to be a part of a plan to eliminate both reporters, the would-be informers of Watergate scandal. His mysterious partner, who set him up and organised the murder of the reporters, was most likely the Comedian himself.
As seen during the boss fight against him, Underboss is extremely physically strong, to the point he could be considered superhuman. He was able to run very fast with a flamethrower on his back, to rip off a metal part of construction site, and had immensely high HP. His fists could send a man flying away. After being defeated by Rorschach and Nite Owl, Underboss was about to reveal who set him up, but was shot in the head by the Comedian and fell to his apparent death. However, a newspaper headline seen immediately after in the game's ending states that Underboss was in a coma and not dead.
Sometime after 1985, Underboss dies at Rikers Island jail complex while engaged in a knife fight over a cigarette lighter.
- He is briefly mentioned in the comic, and is the main villain in the first half of the video game Watchmen: The End is Nigh.