20 Things You Didn't Know About The Xenomorph
11. A Biological Weapon
According to canon, the Xenomorphs were created through the use of a mysterious black goo known as Agent A0-3959X.91 – 15. The liquid, is an extremely potent pathogen containing millions of micro organisms, and had to be contained within specially designed urns to keep it under control.
Agent A0-3959X.91 – 15 was developed by the Engineers (as seen in Prometheus) as a way to cleanse planets of unwanted non-botanical lifeforms, however after mutating it quickly began changing and mutating the organisms it came into contact with, rewriting their DNA and making them mindlessly violent.