Jimmy Cody, Matt's doctor and fellow vampire hunter, gets a fair bit of screen time, but he doesn't necessarily leave a huge impression. Everybody else has some sort of inner life: Ben muses sadly about his wife; Susan's got the fight with her mother; Matt thinks about all his dead students. Even Larry Crockett gets some time to think about whether he really wants to screw over the town.
But Jimmy is mostly about boyish good looks and taking care of Matt and fighting vampires. The one thing you will probably most remember about Jimmy is his gnarly, bloody end on that staircase. You could say that Jimmy's mostly in the book to be Swiss cheese. He's the extra guy you throw down the stairs at the end for one last nasty twist. He's cannon fodder.
Hey, every slasher book needs some.