The Mysterians are a humanoid, sapient species.
With their home planet ravaged by a nuclear war and their species nearing the edge of extinction they invaded the Earth with flying spacecraft, tunnelling mobile bases and a giant robot named Moguera. Their demands to the Earth were land for their species to live on and women to let them reproduce and repopulate.
Individuals were clad head-to-toe in colourful armor, presumably as a life-support mechanism, and each carried handheld energy weapons. Underneath the armor they look strikingly similar to humans, though with mutated flesh.