Little is known of Eugene Tooms' past. He is at least 100 years old, and worked as a dogcatcher thirty years before the story was set. Awakening from slumber, he kills several people and eats their livers. The rooms they were found in all had the doors and windows locked.
He attracts the FBI's attention when he returns to the scene of a crime. He is interrogated, and while he is let to go free, Mulder's suspicions are confirmed. He visits Tooms' residence, uncovering a nest of bile and newspapers. Tooms watches them from above, stealing Scully's necklace as a trophy...she is his new target.
Mulder realizes this when it's almost too late. Tooms sneaks into Scully's house and attacks her. At the last minute, Mulder bursts in and he and Scully capture Tooms. He is locked up, but that's not the end...
A year later, Tooms has been kept in a mental institution, and he's now up for parole. He is granted parole, and everyone believes him to be a normal member of society again...except for Mulder of course. He hounds Tooms incessantly, knowing that if Tooms gets one more liver he will go into hibernation and be unreachable for 30 years. Tooms manages to frame Mulder for brutality, and Mulder is told to stay away from Tooms. He doesn't of course.
Tooms kills his psychiatrist, getting the final liver. He sets up his nest under an escalator. Mulder goes under the escalator to get him, and ends up in a fight with Tooms. He jumps out with help from Scully, and turns on the escalator. Case closed.
Powers and Abilities
Eugene Tooms is a genetic mutant, whose mutations allow him to stretch and contort his bones and muscles to incredible lengths. This grants him the ability to squeeze into almost any space. He uses his power to hunt down his prey, taking five human livers before going into hibernation for thirty years. He is either immortal or extremely long lived.