Created by an unseen holoprogrammer named Felix, Vic is self-aware and knows he is a hologram. He has the ability to turn his program off and on, but his program was allowed to run "26 hours a day" so he could live a real life within the holodeck. Vic works as a singer who resembles Frank Sinatra. He is used as counselor by various crewmembers of Deep Space 9, and he took it upon himself to get Odo and Kira together romantically.
In the mirror universe, VicFontaine appeared to be a real Human rather than a hologram.
It was never explained why Vic was a real solid being, rather than a hologram, in the mirror universe, or why he was fighting the Terran Rebellion.
Some viewers believe that the mirror Vic was a Human; others believe that sparks, smoke and circuits were seen emanating from Vic's chest wound, indicating that Vic was an android based on the same physical template as the holographic Vic in the primary universe.