Magratheans are the Human inhabitants of planet Magrathea. They are taller and thinner than most Humans, on average, probably owing to their evolution in the atmosphere of their native planet. They are most famous for developing the art of custom planet building and making a fortune that destroyed the economy of the Galactic Empire.
Magratheans were commissioned by Mice to create the combined planet and computer, Earth. After it was destroyed by a Vogon Constructor Fleet they began constructing Earth Mark II, but this turned out to be unnecessary.