Former Starfleet medical officer, he worked in several locations as a junior doctor. His last post was on Starbase 375, which was used as the main staging point for the transfer of Dominion prisoners.

During the two years he was at the Starbase, he managed to perform illegal procedures on almost a hundred Dominion prisoners, six of which subsequently died.

After the Dominion war ended, an investigation was started and Gellar's 'experiments' were uncovered. Gellar was sentenced to life imprisonment on the penal planet Ceti-Alpha Five in 2375.

Gellar along with five other former Starfleet officers managed to escape their prison and are still at large.

Gellar requires regular treatment for a rare blood disorder. The drugs that he requires cannot be replicated, meaning he must find a natural source or a medical facility.

Of all the escapee's, Gellar is the most likely to be captured when he seeks medical assistance for his condition.