The mutant Alligator is an enemy in the Resident Evil series.
During the viral outbreak in Raccoon City, survivors Leon S. Kennedy or Claire Redfield encountered an alligator that mutated to a huge size as a result of T-Virus exposure. It uses the garbage dump inside the sewers as its habitat and source of food.
Infected alligators were also seen during the viral outbreak in Sheena Island. Like the one in Raccoon City, these were not deliberately created B.O.W.s, but accidents.
A particularly nasty alligator was found in the "Wild Things" scenario of Resident Evil Outbreak: File 2 (referred to as "Gnaw" in the game's bonus materials), swimming in its zoo habitat that the survivors had to cross. It is assumed that this was an accidental creation when the T-Virus infected the zoo. Although the virus did not change its physical appearance or size from that an uninfected alligator, it did improve its aggression.