Slither is a mutant recruited by Magneto as part of the team Mutant Force.
He would later become one of Viper's followers who joined the Serpent Society to help in Viper's coup against Sidewinder. Slither was fiercely loyal to Viper and remained to her side as a sort of attack dog.
Slither recovers and attacks D-Man, and would have strangled him if not for Nomad's intervention. Nomad interrogates Slither and finds out Viper sent three Serpent Society members to poison the water supply of Washington. The "poison" turns out to be a mutagenic agent based on Slither's own genes, which turns the citizens into snake people.
Slither leaves the Serpent Society after Viper does so.