1: Of or pertaining to the planet Mars or its hypothetical inhabitants
2: A being (presumably intelligent) originating from Mars. Rarely portrayed as peaceful, Martians always seem to desire the conquering or obliteration of Earth.
3: Of or pertaining to Mars, the Roman God of War, or to the planet bearing his name; martial
The antagonists in H.G. Well’s classic science-fiction novel The War of the Worlds