& the Flood.
Its a sentient water borne virus that takes over human bodies it wants to be taken to earth because of all the water there
There's also the Ambassadors of death. Apart from being Ahmadinejad's awesome name for a bomber aircraft, the ambassadors of death were an intelligent race that fed off of radiation. They are not native to Mars, but that is when humanity first encountered them. Apparently we were already sending manned space flights to Mars in the 70s or 80s.