- "All progress has a price. A necessary attitude, I think you'll agree. Logic and truth leave little room for moral posturing."
- ―Kleist (from Aliens: Rogue)
Professor Ernst Kleist was a research scientist for the Z.C.T. Corporation and the director of the company's Charon Base research facility. At Charon, Kleist was the head of Project Chimera, a secret research program that aimed to use gene-splicing to create a human/Xenomorph hybrid creature, the intention being to develop a means for humanity to control the Xenomorphs.
Kleist's genetic experimentation led to the creation of the Rogue, an immensely powerful human/Xenomorph hybrid. However, the Rogue proved not to be the tame organism Kleist predicated, and its escape from confinement initiated a Xenomorph outbreak at Charon that ultimately destroyed the base. Kleist himself was seemingly killed by the Queen that ruled the Hive on Charon.
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 Grace.
While working to undo a plot to steal the secrets of his research and expose his murderous means of experimentation by the Grant Corporation spy known as "John Cray" 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.
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.
Kleist was subsequently, apparently killed when he used a sound cannon on the Queen until it went critical, destroying the asteroid 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".
- The scene where Kleist surveys the failed "docile" Xenomorph Queens, preserved in giant tanks in his lab, is remarkably similar to the scene where Ripley 8 discovers the failed Ripley clones in Alien Resurrection, made four years later.