Ernst Kleist was a scientist and director of Charon Base for the ZCT corporation some time after the Alien infestation of Earth.
Kleist served as the head of Project Chimera, which aimed to exploit all aspects of the Alien's anatomy for human use and use gene-splicing to hybridize a Xenomorph Queen capable of producing controllable Xenomorphs to which could be bio-programmed for any task. Unfortunately, Kleist's research involved quite a bit of preludial experimentation, and in this case the "lab rats" were members of the human staff at the station. Kleist also had a corporate security staff under Larsen, and a contingent of Colonial Marines under Sargeant Green. He had a synthetic personal aid and bodyguard named.
Though Professor Kleist was able to create several domesticated Drones, he was unable to breed any Queens as they all would automatically die upon birth. Frustrated by his failed attempts to breed a Queen, Kleist decided to breed a Xenomorph powerful enough to usurp a Queen. While working to undo a plot to steal the secrets of his research and expose her murderous means of experimentation by the Grant Corporation spy known as "John Kray" and the Charon transport ship captain Joyce Palmer, Kleist discovered that John Kray's genes were by coincidence capable of hosting a new kind of Alien. Hence, Kleist was able to breed a male Xenomorph King Alien (sometimes referred to as The Rogue). Kleist deemed it a perfect evolutionary successor to the Aliens, and hoped to have his King challenge Charon's resident Alien Queen. Kleist believed the Rogue to be more powerful than the Queen.
Professor Kleist unleashed the Rogue upon the base's captive Xenomorph hive in order to test the Rogue of its capabilities, but it soon escaped shortly after it heard the Queen's cries. The Rogue continues to run rampant through the entire Charon Base, killing both Xenomorphs and Humans alike before confronting the Queen. In the final brutal confrontation between the Aliens, with the whole of Charon stations in ruins, the scientist was shocked to find that the Queen was in fact the superior specimen. While the Rogue was larger and stronger, the Queen's superior speed and intellect enabled her to dodge the Rogue's attacks and slowly wear it down and finally slaughter it. Unable to accept defeat, Professor Kleist used a sound cannon on the Queen until it went critical, destroying the Charon Base.
Some time later, a much-mutated Ernst Kleist resurfaced as the leader of a group of mutated human/Alien hybrids called the Bug-Men, their genes altered through use of Royal Jelly, who were terrorizing a section of space in his name. Here, the maddened Kleist went simply by the name of "father".