Martian

Martian
Homeworld	Mars
Skin	Possibly Green, but nearly impossible to tell, as the only known visual representation of them is a hologram.
Eyes	Unknown
Notable Facts	-Extinct -Huge Heads -Extremely Intelligent
[Source]

Martians were a species that were native to the planet Mars. They were an extremely advanced species, as evidenced by their apparent project of transforming their homeworld into a huge spaceship after testing the technology on a nearby planet. Ironically, they worked themselves into extinction doing this, so there are no more Martians living on Mars. The only "Martian" left is the Mars-ship's interactive, holographic instruction manual, which appeared in "Battle of the Planets".

The Martians' most noticeable feature was their enormous head; their eyes, nose and mouth were compacted together on their lower head, while their forehead dominated the other 3/4 of the cranium, suggesting that their brains were unusually large. Their appearance from the neck down is unknown, as only skulls were ever seen.

The Martians also built huge pyramids similar to those in Egypt, as part of their spaceship. However, most do not appear to be part of the spacecraft, and were probably some other form of architecture in days long past. These may also suggest that the Martians could have visited Earth many years ago, as homage to the paranormal theory that aliens helped build the pyramids, but this is never mentioned on the show.