He is best known for his prominent role in
LucasFilm Games'
adventure game Maniac Mansion, and his even-more-prominent role in
LucasArts'
sequel,
Day of the Tentacle. He is appropriately named because of his green
skin color.
Green Tentacle is a creation of the mad scientist Dr. Fred. His primary goal in life seems to be to succeed as a punk rock'n'roll star. He spent most of his on-screen time in Maniac Mansion dealing with chronic depression over never being able to succeed. In Day of the Tentacle, he (ironically enough) devoted most of his time to trembling in a corner somewhere.
He has a band called Green T and the Sushi Platter, and their first cd is titled Rap On The Forehead. They're famous in the club scene for being really loud and featuring a guy who plays power tools.
He has an evil brother named Purple Tentacle. See "tentacle" for general information on the tentacle race.