Martians

"No-one would have believed, in the last years of the 19th century that human affairs were being watched from the timeless worlds of space. No one could have dreamed that we were being scrutinized as someone with a microscope studies creatures that swarm and multiply in a drop of water. Few men even considered the possibility of life on other planets. And yet, across the gulf of space, minds immeasurably superior to ours regarded this Earth with envious eyes, and slowly, and surely, they drew their plans against us.'' ~ War of the Worlds

Martians are powerful alien beings from an alternate-universe in which Earth was attacked by Martian invaders near the end of the 19th century - unlike the mainstream universe, where Mars is generally seen as unable to support life and the War of the Worlds is a popular work of fiction.

Due to their role as guardians of the imagination The Immortals have faced the Martians several times as the alien invaders seek new ways to expand beyond their native universe.