Mercurians are the native species of the planet Mercury.
Biologically, they have adapted to withstand the dangerous gases of the planet Mercury, as well as their home world's proximity to the sun.
In the reality known as Earth-48, Mercurians were a warlike race of hunter/gatherers. They despised the concept of peace and longed for the thrill of the kill. They especially enjoyed sending male hunting parties to other worlds in order to crossbreed with female captives from that world in the hopes of breeding stronger warriors.
The Mercurians were one of nine planetary houses that vied for control over the planet Earth. After Earth's native population decimated itself, it became a sort of staging ground for members of the nine planetary houses to settle disputes, usually physically. It was a Mercurian who first renamed Earth, War World. When the convocation of the nine planetary houses first convened, the Mercurian representative declared a trade dispute against the delegate from Jupiter. Secretly, the Mercurians never supported the peace accord, believing the other eight houses to be populated with sycophants and pacifists.
Some time ago, a Mercurian hunting party came to the War World in need of sport and ran afoul of the Forerunner, Viza'Aziv. She easily decimated the Mercurian ranks, despite the fact that she was three years too young to be engaging in mortal combat.
- Mercurians are portrayed with little consistency. There's no such thing as one single "Mercurian" race.