Doctor Klein was a researcher for the Orochi Group. While he worked for the Orochi, he was assigned to the research facility in the Scorched Desert known as the Ankh. At this point, Klein had already been exposed to the filth over a course of many micro doses. Because of this prolonged exposure, Klein exhibits a certain tolerance to the filth, allowing him to resist its otherwise destructive effects. Despite his tolerance to the filth, Klein's physical appearance has been greatly affected by his exposure.
While Klein claims the Ankh is a laboratory, it was originally an ancient temple. What happened to its previous inhabitants is unknown, but it is likely that they were killed as Klein claims he killed the high priest of Aten and looted his staff, which Klein now wields as a weapon.
Klein was allowed to continue his experiments undisturbed after this incident, which resulted in the deaths of many Orochi researchers who fell victim to Klein's experimentation. This would, however, not last as a team of secretworlders entered the Ankh to investigate by request of the Orochi operative Lisa Hui. Upon entering the Ankh, they were greeted by Doctor Klein himself, who made it very clear that he intended to use them in his experiments. Klein was, however, unsuccessful in killing the secretworlders, and he was eventually slain while trying to unleash a potentially fatal filth chain reaction.
To be clear, I do not need you alive for my experimentation. It is quicker this way, please understand.
I think we shall understand each other better post-mortem.
I have no words! No words!
You people! I told the committee we should have filled Agartha with concrete when we had the chance!
My work will endure beyond this flesh, I am the filth!