Marvin is the ship's robot aboard the starship Heart of Gold. He was built as a failed prototype of Sirius Cybernetics Corporation's GPP (Genuine People Personalities) technology.

Marvin is afflicted with severe depression and boredom, in part because he has a "brain the size of a planet" which he is seldom (if ever) given the chance to use. Indeed, the true horror of Marvin's existence is that no task he could be given would occupy even the tiniest fraction of his vast intellect. Marvin claims he is 50,000 times more intelligent than a human, (or 30 billion times more intelligent than a live mattress(see Zem)) though this is, if anything, a vast underestimation.

When kidnapped by the bellicose Krikkit robots and tied to the interfaces of their intelligent war computer, Marvin simultaneously manages to plan the entire planet's military strategy, solve "all of the major mathematical, physical, chemical, biological, sociological, philosophical, etymological, meteorological and psychological problems of the Universe except his own, three times over," and compose a number of lullabies. He seemed to find this last task the hardest, and only one, "How I Hate the Night", is known.