When picking a public domain superhero to talk about, the name plays a really important part for me. Half the time I just look for a name I find interesting and then do more research. This is all to say that Dr Vampire is one of the more disappointing ones (and yet he's the last one for this year).
His real name is Dr. John Rogers, a... guy. Like most public domain superheroes, he has no backstory other than doing what he does - namely killing Vampires... I think.
Here's the fun twist about Dr. Vampire: I have no clue why he's called that. Is he a vampire? Probably not. Does he hunt vampires? Maybe. His intro panel says he goes after "fiends who thirst for warm, red blood!" which seems pretty cut and dry, but then in his first comic, it's unclear if the person he's hunting is a vampire or just, like, some guy who kills people in a very bloody way.
And it is never elaborated on. Dr. Vampire was in only 1 comic and never showed up again.
Have a good New Year!