Horror movies like The Conjuring, Zodiac, and Frozen Ground are all based on real events and individuals, just as characters like Leatherface from Texas Chainsaw Massacre are based on real people like Ed Gein. It should come as no surprise that video games also take inspiration from real events, as demonstrated by these memorable villains.
Dr. Trager is one of the more memorable Variant villains from Outlast. He is a deranged killer surgeon who hunts down Miles Upshur through the corridors of Mount Massive Asylum. He has surgical experiments that he enjoys performing on others in the asylum, most of which involve removing fingers, tongues, and other body parts.
Trager's name is likely a reference to Milton Trager, who developed what he called the Trager Approach. This involved a process he dubbed Psychophysical Integration, which tried to heal the body through the mind and vice versa. This approach was never widely accepted, however, as it was never quite as effective as traditional medicine.
Despite the Trager Approach's failings, Milton Trager seemed to consider himself a bit of a Renaissance man, as he believed his methods could make him a capable practitioner in any pursuit he undertook. That said, Psychophysical Integration never had results quite as grisly as those achieved by the Dr. Trager of Outlast.
The Baker Family of Resident Evil VII: Biohazard is very openly inspired by the Sawyers of Texas Chainsaw Massacre fame. This is most vividly shown in the iconic dinner scene in Biohozard that resembles a similarly iconic dinner scene in the original Texas Chainsaw Massacre movie.
With this in mind, one is inclined to make one-to-one comparisons, and Jack Baker is most easily comparable to Leatherface himself. This comparison becomes much easier to make during the chainsaw duel between Jack Baker and Ethan Winters.
With Jack Baker having qualities inspired by Leatherface, the comparison can extend to the real-life inspiration for Leatherface, Ed Gein. Ed Gein was a killer and a grave robber who notably made clothing and furniture with leather made from human skin.
This is comparable to the dinner scene in Resident Evil VII, where it very much appears that the Baker Family is eating human flesh. Jack Baker even looks a bit like Ed Gein, albeit with glasses and untamed hair. Though Jack is more clearly based upon Leatherface, that line of inspiration still goes back to the real-life Ed Gein.
Karl Heisenberg of Resident Evil: Village is directly named after a real-life scientist, Dr. Werner Karl Heisenberg. He is most well-known for his work in nuclear physics and his contributions to the German nuclear weapons program in the build-up to and during the Second World War. He was offered an opportunity to emigrate to the United States in 1939, but refused.
Notably, Heisenberg is also renowned for his work in ferromagnetism, which is the study of how certain metals can become permanent magnets under certain conditions. Of course, the Karl Heisenberg of Resident Evil: Village has the power to manipulate metals through magnetism, making this a somewhat obvious link.
Noblewoman Alcina Dimitrescu is the austere and vicious head of Castle Dimitrescu in Resident Evil VIII: Village. She and her daughters are made to resemble vampires, with her daughters, in particular, resembling the Three Sisters from Bram Stoker's Dracula. However, Dimitrescu herself is very similar to the legends of the real-life Elizabeth Bathory.
Bathory herself was a noblewoman who allegedly kept young women as her servants. It's said that she would torture and kill these young girls, and even bathe in their blood to remain youthful. This is all alleged, of course, as there is little surviving evidence of these historic crimes.
As for Dimitrescu herself, there are several notes scattered throughout Castle Dimitrescu discussing the cruel experiments that Lady Dimitrescu performed on her female servants, and this seems to be the means through which she created her daughters.
This point of comparison is a little more esoteric, as there seems to be less of a clear connection between these two other than location, nobility, and the similarities between the name "Brennenburg" and "Brandenburg." That said, the Amnesia Wiki draws comparisons between Amnesia: The Dark Descent's Alexander of Brennenburg and the real-life Frederick III of Brandenberg who would go on to become King Frederick I of Prussia.
The reasons for these comparisons seem to be based largely on the name as well as the fact that Frederick III of Brandenburg became the first king of Prussia. The other point of comparison is that Frederick III of Brandenburg established the Order of the Black Eagle in real life, and Alexander of Brennenburg was a founding member of the Order of the Black Eagle. Again, this comparison may be a bit of a stretch, but there is something there worth looking at.
Andrew Ryan is one of the villains of the first Bioshock game. He is the man that Fontaine sends protagonist Jack to kill, and Ryan himself is the man who founded the libertarian utopia of Rapture. Andrew Ryan's name is a play on the name of Ayn Rand, a mid-20th century writer famous for helping to shape the modern libertarian movement as well as the concept of "objectivism."
Objectivism can be described as an ideology in which all power and wealth in a society is given to the smartest and most capable, something akin to a Darwinist society. Of course, the follies of such an idea are shown by the devastation of Rapture and the misery it ultimately created.