Sidewinder is the name of three different fictional characters appearing in American comic books published by Marvel Comics. The original version was Seth Voelker. A second version appeared in 1998 but was killed during his attempt to infiltrate S.H.I.E.L.D. A third version, Gregory Bryan, was given powers similar to the original Sidewinder by the Brand Corporation.

Seth Voelker started out as an Economics professor before Roxxon Oil Company chemically mutated him and gave him the power to teleport, starting his criminal career as Sidewinder. He initially worked as hired henchman alongside Anaconda, Death Adder and Black Mamba. He later organized the Serpent Society, a group of snake-themed criminals for hire, with the Serpent Society working like a trade union. At one point, Sidewinder was deposed as leader by Viper as several members of the Serpent Society had infiltrated the group to help Viper from within. While Viper was defeated, Sidewinder chose to leave the Serpent Society with King Cobra taking control of the Serpent Society. He later retires from being a criminal.

Gregory Bryan was given his powers by the Brand Corporation and became a member of the Serpent Society later on. He later became a member of Serpent Solutions when the Serpent Society was reorganized.

The original Sidewinder, Seth Voelker, first appeared in Marvel Two-in-One #64 (Jun 1980), and was created by writers Mark Gruenwald and Ralph Macchio and artist George Pérez.

Seth Voelker was born in Kenosha, Wisconsin and grew up to become an economics professor. He failed to make tenure and was hired by the Roxxon Oil Company as an economic analyst. He discovered their criminal schemes and they permitted him to apply for mutagenic alteration. As the professional criminal Sidewinder, he is hired by Roxxon to retrieve the Serpent Crown. Alongside the third incarnation of the Serpent Squad, Sidewinder retrieves the crown and delivers it to company president Hugh Jones. After his stint working for Roxxon, Sidewinder decides to form his own criminal organization, the Serpent Society. In the Society's first mission, Sidewinder dispatches them to kill MODOK on behalf of A.I.M.

Sidewinder is betrayed by his organization after Viper infiltrates the group. After being poisoned, he is aided by Diamondback and the two survive.

Sidewinder retires from villainy to allow Captain America to help him get money for his daughter who was ill with cancer.

Sidewinder comes out of retirement after being hired by the Assassins Guild to target Elektra and her allies.