Gaius Baltar

Battlestar Galactica's Baltar gave away crucial secrets to a Cylon seductress. Because if anyone can be seduced by a robot, it's probably the nerdy guy with a mullet.

Benny

Benny turns heel and goes after Arnold Schwarzenegger's character in Total Recall. We don't want to second guess the writing, but calling your Benedict Arnold character "Bennie" isn't a flash of brilliance.

Dr. Michaels

Dr. Michaels betrays the crew in Fantastic Voyage, attempting to crash their miniaturized ship inside the human body it is exploring. He's pretty much the living embodiment of a hemorrhoid.

Cypher

Cypher strikes a deal with the Agents from The Matrix to backhand the humans. In exchange, he was to receive ignorance. Which makes us wonder if the blue pill can be slipped into Neo's drink, like a reality roofie.

Dennis Nedry

In Jurassic Park, Nedry sells the dino embryos to a competing bidder. Because if anyone should be a master of international genetic espionage, it's the bumbling mailman from Seinfeld.

Carter Burke

Another sitcom regular betrays the cause in Aliens, where Paul Reiser's character deceives Ripley in order to preserve alien samples. It's rare that a character is portrayed as evil because they refuse to drop a nuke.

Obadiah Stane

In the film version of Iron Man, Stane turns on Tony Stark when he declares they will stop making weapons. Stark then defeats Stane, ironically by weaponizing an entire building.

Peter Pettigrew

Pettigrew betrayed Harry Potter's parents and joined up with Lord Voldemort. Hey, there's only so many positions for wizards in the fight against evil in this recession, and Voldemort was hiring.

Elsa Schneider

The sexy love interest from Indiana Jones and the Last Crusade turns out to be a Nazi. We were most concerned that this association would affect his tenure as a professor.

Saruman

The Lord of the Rings wizard leader turns on Gandalf to grab power using an army of orcs. We, personally, would've gone with an army of Ewoks, because Ewoks and hobbits would be a pretty evenly matched battle.

Holly Thompson

Secretly collaborating with the aliens in They Live, Holly tries to shoot "Rowdy" Roddy Piper's character. This was a solid film, but it could have been Oscar material had Piper wrestled a space alien.

Michael Dawson

Hoping to finally stop having to scream his son's name, Michael turns on the survivors in LOST, killing two of them. Because of this, he wasn't allowed to do any fun time-traveling with the rest of the gang.

Valeris

This high-achieving Vulcan turns on the Enterprise crew in Star Trek VI, forcing Spock to mind-meld with her. You don't want to mind-meld with Spock; everything that guy thinks about is disturbingly confusing.

Lando Calrissian

Revealing himself as a traitor, Lando turns Han Solo and Leia over to the Empire, in exchange for thousands of mint-in-box Star Wars toys.

Harmony Kendall

In the series-ending episode of Angel, Harmony blabs about Angel's secret plans. She also helped Anderson Cooper out Buffy as a vampire slayer, which made us wonder why the U.S. government didn't plan to repeatedly nuke the Hellmouth.