Grathon 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, Grathon Tolar was serving in a Klingon prison, awaiting execution for unspecified crimes. It was at this time when Captain Sisko, acting under the guidance of Elim Garak and with the support of Starfleet, arranged for his release from a sentence of death into his custody. Grathon's utility to Captain Sisko was that of his renowned skill 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 Grathon 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 Grathon's unlawful presence on Deep Space 9. Ultimately, Quark did not press charges against Grathon, but only after receiving a substantial bribe from Captain Sisko for compensation.
Subsequently restricted to his quarters, Grathon finished the ersatz recording and proffered it to Sisko and Garak soon afterwards. After being tentatively accepted by Captain Sisko, Grathon 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.
After Senator Vreenak rejected the recording as a fake and left to return to Romulus, Grathon Tolar was not seen again. Having never received his leave by Garak, he was presumed to have been murdered and disposed of soon thereafter. (DS9: "In the Pale Moonlight")