Commander William Riker (Jonathan Frakes) and Counselor Deanna Troi (Marina Sirtis) are the only two Star Trek characters who have appeared in three series finales. Introduced onStar Trek: The Next Generation, Riker and Troi served alongside one another on the USS Enterprise-D of Captain Jean-Luc Picard (Patrick Stewart). The TNG premiere established that the two Starfleet officers had a previous romantic history, and they went on to have one of Star Trek's greatest love stories. Riker and Troi eventually married, and the former took over command of the USS Titan.