Brett Colby is or was a vampire executioner whose home base is unknown.
About three years before the events of Circus of the Damned Colby got called to Elbert, Wisconsin, a small town Larry is from. There was a string of vampire attacks, leading to the death of 12 people. Colby put stop to it by tracking down and killing five vampires.
Larry never met the man personally, being away at college at the time, but Larry's parents were very impressed with Colby, and the event inspired Larry to become a vampire hunter as well. The number of the victims was large enough that it made the papers, and Anita recognizes the story right away when Larry tells it to her, and even remembers where it happened.