Former teacher of Henry Frankenstein at Goldstadt Medical College, Dr. Septimus Pretorius was a tall, emaciated-looking man with an unusually large nose and devilish pointed ears. A professor of philosophy, it was Pretorius who first pointed young Henry on the path to his unwholesome experiments with giving life to the dead, and when the horrors of the Frankenstein monster were traced from Henry back to Pretorius, Pretorius was fired.
Pretorius performed experiments similar to Henry's, creating life in the form of various miniature people in bottles, which he claimed to have grown from "seed." He sought his former student out after learning that the Frankenstein monster had survived the fiery inferno of the burning windmill, and proposed to Henry that together they create a mate for him, with Henry building the body and Pretorius supplying an artificially-grown brain. Henry initially balked at the idea, but Pretorius had an ace up his sleeve: He had encountered the Frankenstein monster within a crypt while he and his two assistants Karl and Ludwig were robbing graves, and told his pupil's creation about his plan to make a mate for him.
The monster, eager for companionship of any kind, considered Pretorius his friend from then on was willing to do anything that the impish scientist desired, such as kidnapping Henry's wife Elizabeth in order to force him to help Pretorius. Henry agreed, and together the two scientists created the bride of Frankenstein. Unfortunately, even the bride found her would-be husband ugly, and the heartbroken monster decided that they all belonged dead and destroyed the laboratory. Although Henry and Elizabeth escaped, Pretorius was killed when the tower exploded.
In the short story "The True History of Dr. Pretorius" by Paul J. McAuley, Pretorius is revealed to be incredibly long-lived, possibly immortal. He claimed to have assisted in experiments beyond those of Henry Frankenstein, including those of Dr. Moreau, Dr. Henry Jekyll, and Henry's ancestor Victor Frankenstein.