The Vega Brothers consist of two men (at least they're the only two that we're aware of so far) - Vincent and Vic. Vincent appeared in "Pulp Fiction" and was portrayed by John Travolta. Vic (aka Mr. Blonde) appeared in "Reservoir Dogs" and was portrayed by Michael Madsen.
During interviews, Quentin Tarantino had made mention that the two Vegas that you saw in the two movies were really supposed to be brothers. A whole flurry of rumours followed about how there would be a movie on the two (which would have to be a prequel to both, I suppose). Tarantino recently confirmed that he had plans for such a movie but it would be way down the line since he's got other committments right now.
"If you're talking like a bitch, I'm gonna slap you like a bitch!" - Vic Vega
"We should have shotguns for this." - Vincent Vega