Marvin the Paranoid Android
Marvin the Paranoid Android is a character in The Hitchhiker's Guide to the Galaxy. He is a robot with a brain the size of a small planet, but also suffers from paranoia, boredom, and ineffable depression. He is first found in the series on the spaceship the Heart of Gold with the infamous improbability drive. His main problem, or so he claims, is that he has such a vast brain power, but never has the opportunity to use even a small fraction of it.
As soon as the members of the crew of the Heart of Gold begin to travel in time as well as space, Marvin is consistently left behind, usually to distract the enemies that are chasing them. In the novel Restaurant at the End of the Universe, Marvin is found in the parking lot at the Restaurant, having waited for them for several million years. By the novel So Long and Thanks for All the Fish, Marvin is close to a billion years old, and finally dies in the arms of Arthur Dent and his lover Fenchurch on their way back from seeing the last words God said to his creation.
In the 2005 film, Marvin's dulcet tones are played by the brilliant Alan Rickman.