Marvin the Paranoid Android is a character from Douglas Adams' Hitch Hiker's Guide to the Galaxy. He is a prototype of the Sirius Cybernetics Corporation's GPP feature. Naturally, in accordance with the Sirius Cybernetics Corporation's track record with all things robotic, Marvin's personality is terminal depression. Part of the humour of Adams' work is the monumentally excessive responses Marvin has to everyday life.
Classic Marvin Quotes include: "Life! Don't talk to me about life! Pardon me for breathing, which I never do anyway so I don't know why I even bother to say it. Oh god, I'm so depressed!", and "Here I am, brain the size of a planet, and they get me to take you down to the bridge. Call that job satisfaction? 'Cos I don't."
Note that although Zaphod Beeblebrox calls him the Paranoid Android, he isn't really paranoid at all.