Tolar was a skilled holographic forgery artist, con-man, and general degenerate in the temporary employ of Starfleet for the ultimate purposes of bringing the Romulan Star Empire into the Dominion War on the side of the Federation.
In 2374, Tolar was awaiting execution in a Klingon prison for unspecified crimes. It was at this time when Captain Benjamin Sisko, acting under the guidance of Elim Garak and with the support of Starfleet, contacted Chancellor Gowron to arrange a pardon. Under the terms of his parole, Tolar was to stay away from the Klingon Empire and create a holo-program for Sisko. Tolar was renowned for his skills in holographic forgery which Sisko wished to put into use to create a faux recording of a high-level Dominion meeting in which the supposed plan for the invasion of Romulus was discussed.
However, before Tolar could complete the recording for Sisko and Garak, he was involved in an altercation in Quark's with the proprietor and M'Pella, one of Quark's Dabo girls. Consequently, this brought the attention of station security as well as the potential for reports and documentation revealing Tolar's presence on Deep Space 9. Ultimately, Quark did not press charges against Tolar, but only after receiving a substantial bribe from Captain Sisko for compensation.
Subsequently restricted to his quarters, Tolar finished the ersatz recording and proffered it to Sisko and Garak soon afterwards. After being tentatively accepted by Captain Sisko, Tolar was rebuffed when attempting to excuse himself -- his freedom was not his own until his recording had been accepted by the Romulan officials it needed to fool.
Ultimately, Tolar's forgery did not fool the Romulan senator Vreenak. After Vreenak left Deep Space 9 to expose the "vile deception" to the entire Alpha Quadrant, his shuttle exploded, killing Vreenak and his staff. An investigation by the Tal Shiar pointed to Dominion sabotage, and the recording was accepted as genuine, with the imperfections in the forgery being attributed to damage from the explosion. Known only to Sisko and Garak at the time, Garak had actually placed a bomb on board Vreenak's shuttle, suspecting that Tolar wasn't up to the job they needed him to do. Tolar was killed by Garak so there would be no witnesses to the operation.