Little is known of this race. The p

Little is known of this race. The principal theory of their connection to the Xenomorphs, which was mentioned briefly by Ridley Scott in his director's commentary for the first Alien DVD, is that the Engineer's Ship in Alien was a "bomber" and that they used them as biogenic weapons to fight an ancient war against an unknown foe. There is some evidence to support this, such as the Xenomorph's biomechanical nature. Xenomorph Eggs were believed to be used as "bombs" on an enemy planet and then the Xenomorphs would proceed to kill the entire population as they spawned.

In Prometheus, it is shown that a lone Engineer was responsible for the creation of the human race. He sacrificed himself as his people left the empty Earth, drinking chemicals that dissolved him and changed his DNA to the planet's first micro-organisms. Humanity soon developed, making the Engineers the ancestors of the human race. As such, Human DNA and Engineer DNA are virtually identical. The lone Engineer's reasons for doing this is unknown, though it seems his race did not hold any positive regard for their descendants. Dozens of cargo ships carrying the weaponized black liquid were set to launch for Earth to release the pathogen and let it wipe out humanity; only to see the Engineers somehow lose control of their intended weapons and perish. The crew of the USCSS Prometheus believed that the abandoned planet they explored was an outpost for weapons engineering and development, lending credence to the theory that the Engineers created the Xenomorphs (or perhaps more specifically, the Black Liquid that led to the Trilobite) for war and genocidal purposes.

It was also noted by the crew of the Prometheus that the Engineers on LV-223 had been dead for around 2,000 years. This has led fans to speculate that up until about 2,000 years ago Engineers were on good terms with humans, but a specific event occurred which caused them to become hostile towards humanity. This explains the cave drawings "inviting" humanity to track them down.

It is also possible that the Engineers had seeded the Earth with human life to create a "breeding ground" for the Xenomorphs.

Speculation has it that the Engineers may have been antagonists / antagonized by the Yautja. In Aliens vs. Predator: Requiem, an Engineer helmet is shown as a Predator war trophy. It is also speculated that the Xenomorphs may have been an Engineer weapon against the Yautja. In the Fire and Stone comic series, a Yautja called Ahab developed an obsession with the Engineers and later battled one - emerging triumphant after using his self-destruct device to kill the Engineer - later claiming its skull as a trophy.