Francis Klum was sexually abused by his older brother, Garrison, and forced to use his mutant powers to help him commit various crimes. Garrison became a drug dealer known as Mr. Brownstone (a reference to a Guns N' Roses song). Though Garrison was himself a mutant with similar teleportation powers, he forced Francis to use his hypnotic abilities to influence clients to buy drugs from him. When two of Garrison's clients overdosed, the Black Cat followed evidence back to the Klum brothers. Francis eventually killed his brother to prevent him from raping the Black Cat. The Black Cat was jailed for Garrison's murder, but Francis teleported her from her cell. He learned that she was also a victim of sexual abuse, and felt a connection with her that he had never before experienced with another person. However, Spider-Man appeared, and because of his former romance with the Black Cat coupled with the bridge being the setting of Gwen Stacy's murder, he lost control, humiliating and permanently scarring Francis physically. Following his confrontation with Spider-Man, Francis bought Mysterio's costume and equipment from the Kingpin and set out to exact revenge on Spider-Man.
Francis Klum was created by Kevin Smith and Terry Dodson and first appeared in Spider-Man/Black Cat: The Evil That Men Do #1 and became Mysterio in the final issue of the miniseries.
Major Story Arcs
After Spider-Man's unmasking to the public, Klum decided to attack the school Peter Parker worked at to get revenge on Spider-Man. Daniel Berkhart, who was also calling himself Mysterio, arrived and allied with Spider-Man to defeat Klum. The two Mysterios were then confronted by a third Mysterio - the demonic spirit of the original Quentin Beck. Francis was critically wounded by Ero, who was infiltrating the school as it's nurse Miss Arrow, who punctured him through the chest with her stingers. Coughing up blood, he teleported to safety. It has been suggested that Ero's venom is fatal to anyone who isn't Spider-Man, so while Francis Klum is most likely deceased, his body has not been found.
Old Man Logan
The Earth-807128 version of Klum as Mysterio creates in Wolverine's mind the illusion of the X-Men's mansion being ruthlessly attacked by an army of super-villains, whom he brutally kills. After the massacre is over, the person Wolverine believed to be Bullseye is revealed to be Jubilee, and he realizes with horror, that he has killed that divergent Earth's X-Men.