Who voices this alien that Marge reveals to have had a one-night stand with and got impregnated with Maggie?
Treehouse of Horror IX:  This is the ninth "Treehouse of Horror" episode, and, like the other "Treehouse of Horror" episodes, contains three self-contained segments: In "Hell Toupée", Homer gets a hair transplant and is possessed by the spirit of an executed criminal; in "Terror of Tiny Toon", Bart and Lisa are trapped in a special, extremely violent episode of "The Itchy & Scratchy Show"; and in "Starship Poopers", Marge reveals that Maggie is the product of a one-night stand with the alien Kang. Kang and Kodos:  Kang is voiced by Harry Shearer and Kodos by Dan Castellaneta.
Harry Shearer