Martian

A Martian was an inhabitant of the planet Mars.

Usage
The term "Martian" was often used jokingly by humans for aliens, much like "flying saucer" was used as a generic term for alien spacecraft. For example, Donna Noble referred to the Doctor as a Martian before finding out about his origins as a Gallifreyan. (DW: The Runaway Bride)

Daniel Llewellyn thought that the Sycorax were from Mars until Major Richard Blake told him that Martians looked completely different. (DW: The Christmas Invasion)

Patrick also initially thought that the Centuripede came from Mars to read other people's mail. (K9TV: The Last Oak Tree)

Native Martians
Several native Martian creatures, such as the Ice Warriors, evolved on Mars, (DW: The Ice Warriors) as did many other Martian lifeforms, such as Martian fungi. (DW: The Seeds of Death) There was also a native virus present on Mars. (DW: The Waters of Mars)

Humans as Martians
By the 22nd century, Mars had been colonised by humans, who pushed the native Ice Warriors into poverty. (PDA: Fear Itself) Once Humanity had made Earth itself uninhabitable, the Usurians saw to it that the Humans could move to Mars. (DW: The Sun Makers)
 * For a more detailed history of Human colonization of Mars, see the separate article on Mars.