Reily served as navigator aboard the U.S.S. Enterprise, under the command of James T. Kirk. Early in his life, Reily witnessed the massacre of his parents, and 4,000 others, on Tarsus IV by Kodos the Executioner. While serving aboard the Enterprise in 2266, during a performance of Hamlet, Reily witnessed the death of Kodos, who went by the alias of actor Anton Karidian.