Manbearpig

Manbearpig is a fictional monster from South Park. According to Al Gore, he is a creature who is "half man, half bear, and half pig" and wanders the earth randomly killing everyone he sees. According to Gore, he is the single biggest threat to humanity today. Obviously, this is completely absurd and untrue, as a parody of Al Gore's claims about Global Warming.

Overview
He appears as the main antagonist in the episode that's titled after him, "Manbearpig". In this episode, after being trapped in Cave of the Winds by Al Gore, the boys must find and kill Manbearpig, but they can't see him.

Manbearpig returns in the "Imagionationland" Trilogy as the main antagonist. When the portal between Imaginationland opens, Manbearpig rampages in a government laboratory. Manbearpig kills various people, including Kyle. Fortunately, however, Cartman successfully revives Kyle, but only to later force him to suck his balls. Manbearpig is sucked back into Imaginationland, but pulls Stan with him. Al Gore pores over security footage and uncovers evidence of Manbearpig's existence. Upon learning this, he declares that the imagination must be nuked. The government agrees, but only because Imaginationland has a terrorist connection.

Manbearpig is later seen in the battle for Imaginationland in the climax of the trilogy. However, his ultimate fate remains unknown. Manbearpig was likely killed by the nuke, but Butters presumably brought him back to life along with everyone else in Imaginationland.

Trivia

 * The design of Manbearpig bears a strong resemblance to Katahdin, from the 1979 horror film, The Prophecy.