“Soon, this foul city will be one giant, glorious swamp!”
Dr. Viper is a half kat, half snake mad scientist who was once Dr. Elrod Purvis, an unremarkable biochemist who worked at Megakat Biochemical Labs. He helped Dr. N. Zyme create Viper Mutagen 368, then tried to steal it to sell to the highest bidder. Zyme, however, caught him, and a fight broke out, which ended with Purvis taking a fall down a flight of stairs and spilling the chemical on himself. He was believed dead, but instead the mutagen mutated him into a half cat-half snake. Purvis went to live in Megakat Swamp and named himself Dr. Viper, and since then has tried repeatedly to take over to turn Megakat City into his own swampland (alternatively referring to it as either “Megaswamp City” or “Mutation City”).
Viper’s first appearance on the scene in Megakat City had him mutating his fellow evil-doer Morbulus into a giant bacteria monster and using him in an attempt to stealKatalyst 99 from Megakat Biochemical. Later, he took over the Megakat Towerwith his army of plantimals, placing a gigantic spore pod on the roof so that it will explode and shower the city with spores, turning it into a swamp. Viper teamed up with Dark Kat and the Metallikats in a bid to destroy the SWAT Kats but their alliance fell apart because the villains cannot work together. When Dark Kat failed to suicide-bomb the SWAT Kats, his lair blew up, but somehow Viper survived. Not long after this Viper flooded Megakat City with a chemical called Katalyst X-63 in a second attempt to turn the city into a swamp. This time he nearly succeeded, but the SWAT Kats able to retrieve the anti-mutagens from Megakat Biochemical and restore the city to normal, despite T-Bone being mutated and Viper using the Katalyst on himself to become a skyscraper-monster.
Dr. Viper was voiced in all five of the episodes he appeared in by Frank Welker.