He is the main
villain in
LucasArts' popular
adventure game Day of the Tentacle. He is, quite appropriately, named for his purple
skin color.
Purple Tentacle always had a mean streak about him. More specifically, he harbors an intense hatred for human beings. His rage is especially centered on his creator, Dr. Fred, whom he detests for having created him so impaired. But his genetically impotent appearance (a suction cup for feet and no arms) severely hindered his ability to do anything about his frustrations.
That is, until he drank the sewage spilled from Dr. Fred's bizarre contraption, the Sludge-o-Matic (a machine whose only purpose, apparently, is to produce tons and tons of toxic waste for no readily explored reason). The toxic ingredients in this foul chemical soup resulted in a genetic mutation. Not only did it result in a physical metamorphosis (Purple grew arms), but it also attacked his brain and enhanced his pent-up rage and resentment a great deal.
Suddenly, Purple was in a position where he could finally wreak his revenge on his creator, and humans in general.
He starts off innocently enough by tipping a few cows. Soon, however, he steps up to stealing a national treasure (a precious diamond), then claims he captured the thief and gives the diamond back to the state. He is hailed as a hero, and from that point on, ends up proclaiming himself ruler of Earth, the tentacles as the master race, and orders the enslavement of all humans on the planet.
It is then up to übergeek Bernard Bernoulli and his two semi-braindead roommates, Laverne (a psychotic med student) and Hoagie (a roadie whose favorite pasttime is biting the heads off rats onstage), to save the world from the tentacle menace.
Not bad for a little slimy megalomaniac, eh?
He also has a brother, Green Tentacle. See "tentacle" for a more thorough description of the tentacle race.