Release him? I have spent an entire career trying to prove that aliens exist... now he's my proof! Dead or alive, he's staying with ME!!
~ Dr. Elliot Coleye of his intentions.
Dr. Elliot Coleye is the main antagonist of the 1999 live action film, My Favorite Martian. He is the head of SETI, who plots on tracking down a martian named Martin and use him to prove the existence of aliens to the world.
He was portrayed by Wallace Shawn, who also played Vizzini in The Princess Bride, Gilbert Huph in The Incredibles, and Taotie in Kung Fu Panda: Legends of Awesomeness.
Coleye first appears at a landing site of an unknown alien ship with his men, where he spots a cigarette covered in alien spit. Despite getting some tracings of an extraterrestrial ship, Coleye is angered to see that the ship is nowhere near the site, thus it cannot be proved that it has ever landed on Earth.
However, Coleye learns that the cigarette belongs to a reporter named Brace Channing, so he has her taken into interrogation, where she offers to help him catch evidence of an alien residing on Earth. Brace manages to deliver the evidence of a Martian named Martin (recorded on several tapes by her former co-worker Tim O'Hara, the protagonist of the film) and attempts to air them on the news. However, Tim, who takes a liking to Martin, manages to retrieve the tapes back and has Martin disguise himself as Brace in order to broadcast another news report to cover the tracks.
Despite Tim's success, Martin almost gets himself exposed during the broadcast, which is watched by Coleye and his men. As Tim and Martin escape from the news station, Coleye and his men give chase to them, deducing that Martin is the Martian who crash-landed on Earth. Despite Tim and Martin's attempts to escape, Coleye manages to get one of his men to fire a tranquilizer dart at Martin, much to Tim's shock.
Coleye and his men then proceed to take both a comatose Martin and Tim into custody at SETI HQ, where he is performing experiments on the former while keeping the latter locked up in a cell. At the lab, Tim tricks one of Coleye's scientists into growing Martin's ship to normal size, breaching security and allowing Tim's friend Lizzie and Martin's talking synthetic suit Zoot to free Tim and defeat two of the guards.
Just as Coleye is about to perform open autopsy on Martin (who has succumbed to his death to the tranquilizer), Lizzie arrives impersonating a surgeon, allowing Tim to use two defibrillators to shock Coleye into unconsciousness. Lizzie then joins Zoot and Martin together, allowing the former to revive the latter, much to Tim and Lizzie's delight. Tim and his friends then escape from SETI HQ, and just as Martin and Zoot are about to escape in their ship, Coleye (having recovered from his shock) arrives with a gun, saying that he spent a lifetime trying to prove the existence of aliens and that he'll do whatever it takes to prove his point to the world, even if it means taking Martin prisoner, dead or alive.
Just as Coleye attempts to shoot Martin with his gun, a SETI official named Armitan (who is actually Martin's old Martian friend Neenert, who has been stuck on Earth since 1964) saves Martin by destroying Coleye's gun with his telepathic power. Martin and Neenert then use their telepathic powers to toss Coleye wildly in the air. Martin, Zoot, and Neenert then board on their ship, flying away back to Mars, much to Coleye's distraught and anger.
Despite the aliens having escaped, Coleye notices some nerplex (an alien gum that can transform anyone into another life form) left by Neenert, and realizes that he can still prove his point with it. Despite Tim's warnings, Coleye consumes the piece of the nerplex, and sees himself changing into a Martian, much to his excitement and delight. While laughing at this, Coleye accidentally swallows the nerplex, which presumably leaves his new form permanent, much to his dismay. Now branded as an extraterrestrial alien, Coleye ends up getting caught by his own men and gets tranquilized off-screen. He is presumably taken into custody and ends up being subjected to experimentation by his organization. As such, Coleye has somehow succeeded in his plan to prove the existence of aliens to the world, but not in the way as he expected.