Underboss was a powerful criminal boss who was "brought down" by Rorschach and Nite Owl II in '65, during their time as partners. 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.
In 1965, he was captured in his hideout, located in sewer, and was put in prison. In 1973, however, he broke out of Sing Sing during a riot (with the help from Jimmy the Gimmick), but was set up for the murder of Woodward and 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.