Martian

A Martian is an inhabitant of the planet Mars. 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 refered to the Doctor as a Martian before finding out about his origins as a Gallifreyan. (DW: The Runaway Bride) 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) Martians look completely different from the Sycorax. (DW: The Christmas Invasion) 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.