Space jockey

    The creature encountered in the derelict spaceship on Acheron had what may have been a nose extending

 vertically down a broad chest. The mouth was present under the beginning of the nose and seemed to have two either mandibles or tusks at the sides of the mouth. Arms are visible to its sides and the alien-being appeared to have been engrafted into his seat. The lower body of the creature was obscured by its seat and was not observed.

Seen elsewhere, living examples of this alien species are shown to be gray or brown skinned, hairless and humanoid, with two arms and legs, and said to have staring, "dead seeming" eyes. Their pupils are in the shape of oblong plus-symbols. The species is thought to have telepathical powers, i.e able to read others thoughts, and capable of projecting its own thoughts to others of its own kind probably. The distress signal is also experienced as a bright and blinding flash of light by humans.

 Mala'kak , Space Jockey, or The Pilot. These are all names given to this species, as well as their scientific name, thought of as "'Mundus gubernavi" or "Universal Pilot." Little is known about these creatures but they are theorized by some to have been the creators of the Xenomorphs or "Alien" and are supposedly experts in the field of Bio-engineering. According to one theory, the Pilots were thought to have created the Xenomorphs as a biological weapon against the Yautja's (predatory alien species) much as various humans themselves would plan to do after first encountering the Xenomorphs on Acheron--and that the Xenomorphs were used to end a civil war, which apparently went horribly wrong. This theory also explains the large amount of alien eggs in the ships cargo bay under the security field. Either way, the only crew member found was the captain and was discovered with ribs protruding outward, showing that a Xenomorph chest burster had been implanted.

Thirteen to fifteen years after the destruction of the Hadley's Hope colony on Acheron, a still-living member of this species established contact with the young woman known as Billie, while rescuing Billie and her comrades on their mission to the Xenomorph homeworld. A childhood survivor of another Xenomorph infestation on the planet Rim, Billie shared with the Pilot a longing for revenge against the entire Xenomorph species. The Pilot followed them back to Earth, where it revealed to Billie its new plan to use Earth's own xenomorph outbreak to conquer the planet.

The Pilot used the power of its ship--identical to the derelict on Acheron--to begin terraforming the Earth, lowering the temperature worldwide. The human government made contact with the Pilot, sending the President of the United States and other representatives to the ship to negotiate terms of surrender. Sensing betrayal, the Pilot attacked the President's party. Swallowing a capsule, the President appeared to have triggered the birth of a chestburster gestating within him, which promptly attacked the terrified Pilot. A signal was sent, and the Pilot's ship was destroyed by nuclear warheads.

Not much is known on how the space jockey ship crashed or what it was doing with the alien eggs in it's hull, but there is a theory:

A space jockey was collecting Xenomorph specimens on Xenomorph prime when he was ambushed by a Facehugger and tried to return home as fast as possible, but didn't make it and the chestburster killed him. The ship crashed on LV-426 and the Alien eventually became a Queen. It then began to form a hive by laying eggs (the eggs Kane found), but since there were no life-forms to be hosts, the eggs remained dormant and the Queen died or went dormant.

