https://sentinelswiki.com/index.php?title=Plague_Rat#tab=Comic_Books:_Plague_Rat

Many decades ago, a foul drug-dealer controlled large swaths of the Rook City drug market. He made his hideout deep in the Rook City sewers, keeping his stash safe from competitor and law enforcement alike. However, his criminal enterprise was worn down by a long battle with a new criminal organization taking control of the city. Over time, he was entirely ousted from the streets of Rook City, and lived in the sewers to survive. Years of handling the vile drugs he sold, mixed with the toxic waste from the industrial plants, slowly twisted and mutated the dealer into a giant, hideous, rat-like monster. Now, his last shreds of humanity all but eliminated, he takes the Rook City sewers in search of his next meal, infecting all he touches.