Jessica Jones Season 1 had a single villain, and all roads and plots lead back to one person: Kilgrave. Season 2 has been more convoluted with fans trying to identify who the real "Big Bad" of the season will turn out to be. Our first clues took Jessica to "IGH," the front for the company who paid her medical bills. That lead her to "Dr. Leslie Hansen," who was dead, and her identity co-opted by a fellow powered person. Now, she's taken another step. Who is Dr. Karl In Jessica Jones Season 2? Will he turn out to be the Big Bad of the season, or is he merely a red herring?
Dr. Karl was originally posted in the casting calls for Season 2 as "Dr. Kirby," with the character's description as "60s, male, open ethnicity, scientist & freethinker SERIES REGULAR – ONE YEAR DEAL." But fans weren't fooled. Gossip quickly spread that this was actually Dr. Karl Malus, a mad scientist from the Marvelverse, and the man responsible for the creation of Nuke (aka Will Simpson) in the comics, as well as the likely head of IGH.
First introduced in the 1980s comic Spider-Woman #30, Dr. Karl was a figure who faced off against Captain America a few times in comics as well as Cap's friend, Sam Wilson. Dr. Karl is involved at times with characters from the Defenders universe. In the comics, he goes after Daredevil in hopes of studying him, and Misty Knight (from Luke Cage) is instrumental in helping Captain America eventually take the doctor down in the All-New, All-Different Marvel series.
In most comics though, his work on trying to experiment on powered people — and sometimes heal them as their powers wane — lead to his most terrible crimes, as well as creating some of Marvel's more obscure powered people. That makes him a really useful character for the Netflix MCU, where the more offbeat powered people seem to reside, especially if it turns out he's the one who gave Luke Cage and Kilgrave their abilities as well.
This also ties in Will Simpson's character, who in the comics is called "Nuke." (The show never makes that connection explicit.) In Season 1, the show seemed to suggest it was Dr. Kozlov who had made Will into what he was, but it looks like Kozlov was merely working for Dr. Karl.
The real question though is how Dr. Karl will tie into Jessica's world, and how many of our characters he actually is responsible for... as well as who our Big Bad is. The fact that Dr. Karl seems to be having an affair with her (and her dedication to him) has no real equivalent in the comic series that my research can find unless she's supposed to be an evil play on She-Thing.
She-Thing, in the comics, is actually a wrestler, Sharon Ventura, who Dr. Karl drugs to turn into a woman of super size and strength. It's suggested in the comics that he also rapes her and keeps her under his control via drugs. When she finally escapes his clutches, she goes on to become the first Ms. Marvel. Our Big Bad, played by Janet McTeer, is certainly under Dr. Karl's control, but her solo scenes playing the piano suggest she's got her own free will and is choosing to be this way without any help from the doctor.
It would be an interesting twist if our supposed Big Bad turned out to be someone under the mind control of an evil man, much like Jessica was last season. It would also be an interesting twist that instead of trying to escape, she's embraced it.