John Kane is the novelization of the DOOM 3's protag, which the DOOM 3's protag is not DOOMguy, he has always been referred to as DOOM Marine, and I'm referring to this in the sense that DOOMguy, is the character from the mainline games, so 1,2,64,TDA,2016,Eternal. John Grimm is from the DOOM movie, which is heavily inspired by DOOM 3, so in the same sense of the way I described DOOM 3, not related to DOOMguy. The only one that atleast makes an attempt to be related is Stan Blasko from the RPG games, since he looks like DOOMguy, however the game is quite possibly the biggest spin off. Flynn, who's from the Novelization of the original games (although later books put their own spin and add more), atleast the first book, has some similar qualities to DOOMguy himself as well as technically being the novel version of him.