Tarl Posset was a Starfleet security officer who was assigned to a Federation space station in the 24th century.
After Deep Space 9 was placed under Federation stewardship, Posset was one of two security officers who Odo established contact with, the other being Joe Simko. Aidan Thorn, who knew Posset from Starfleet Academy and served with him at the dilithium processing center on Butera V, thought that Posset was glad that he had dealt with Odo while others hadn't, due to the valuable information that Odo provided him. (DS9 novel: Saratoga)