Xichak, from Martian Dreams
Xichak was the naturalist for the Elysium grove on Mars, and one of the Martians who escaped to the Dream-World when Raxachk's plague was unleashed. When the humans arrived and used Elysium's Dream Machine, Xichak temporarily took over the body of Wyatt Earp.
When the Avatar met Xichak in Martian Dreams, he explained much to the hero about the various martian lifeforms, including the Rockworms, Ammonoids, and Canal Worms. Having explored much of the surface of Mars, Xichak also knew that the polar icecaps were likely the best current method of retrieving water on Mars.
After Wyatt Earp's mind was restored to its body, Xichak's mind was transplanted into a robotronic body, along with the other Martians. Xichak is likely still living somewhere on Earth.