The Giant Leech is a mutated leech that appears in the video game Resident Evil: Outbreak. It appears during one of the game's scenarios: The Hive.
This leech is not at all the same as the leeches that were produced by James Marcus. This creature was a normal leech that lurked in the sewers of Raccoon City and was accidentally infected with the T-virus during the Raccoon City Destruction Incident. The virus caused the creature to grow to tremendous size, about the size of an adult human. Unlike most T-virus mutations, this leech did not become highly aggressive and, for the most part, ignored most creatures that kept their distance.
The giant leech was encountered by a group of survivors in the waterways beneath Raccoon General Hospital. Blocking the survivors' path, the creature only attacked itself when it was provoked, letting its smaller leech offspring attack and feed on the warm-blooded humans. Several leeches had also infested the body of a doctor from the hospital and used his body as a vehicle to attack would-be prey. Steering clear of its tentacles and poisonous bites, the survivors were able to destroy the queen leech by luring it close to a line of gas drums and then detonating them.