Riley and his family lived on the Tarsus IV colony in 2246. In that year, a massive food shortage struck the planet, leading Governor Kodos to institute a eugenics program in which he personally selected 4,000 colonists to be executed, thereby ensuring enough food for the survivors. Amongst those killed were Riley's father and mother. (TOS: "The Conscience of the King")
By 2266, Riley was serving as navigator aboard the Enterprise as a lieutenant. In that year, Riley was one of the first crewmembers to fall victim to an unusual disease which caused those affected to act out and lose their inhibitions. Under the disease's influence, Riley commandeered the ship's engineering section, and rerouted all command functions there, prohibiting the rest of the crew from controlling the ship. This posed a significant danger to the Enterprise, as it was locked in an unstable orbit of the planet Psi 2000, and in the process of spiraling down towards the surface. Proclaiming himself "Captain Kevin Thomas Riley," he deactivated the ship's engines and regaled the crew with repeated renditions of the song "I'll Take You Home Again, Kathleen." Eventually, Captain Kirk and crew were able to regain control of the ship, and institute a full-power restart of the engines, narrowly avoiding destruction of the Enterprise. (TOS: "The Naked Time")
Later that year, Riley was serving in the communications section of the Enterprise. When Captain Kirk came to believe that an actor which had been brought aboard the ship was, in actuality, Kodos the Executioner, who had murdered Riley's family twenty years previously, he had Riley transferred back down to the engineering section in an attempt to keep Riley out of harm's way. Riley, who was unaware of Kirk's true motivations, viewed the transfer as a demotion, as he had previously been transferred up from engineering. Despite Kirk's attempts to protect him, Riley was almost killed by Lenore Karidian, Kodos's daughter, who was attempting to eliminate all survivors of the massacre who could identify Kodos. After surviving the attempt on his life, Riley learned of Kodos's presence on the ship, and attempted to take revenge by killing him with a hand phaser, although he was eventually talked out of the attempt by Kirk. (TOS: "The Conscience of the King")
|Navigators of the starships Enterprise|
|USS Enterprise:||Arex • Bailey • Brent • Chekov • DePaul • DeSalle • DiFalco • Farrell • Hadley • Haines • Ilia • Kelso • Latimer • Leslie • Osborne • Painter • Riley • Stiles • Saavik • Tyler • Uhura|
|USS Enterprise (alternate reality):||Chekov • Darwin|
Kevin Riley was portrayed by Bruce Hyde.
In the screenplay of TOS: "The Conscience of the King", the character whose parents were murdered by Kodos was named "Lieutenant Robert Daiken". However, when Hyde was cast in the role, they renamed the character to fit with his previous appearance as Riley in TOS: "The Naked Time". This explains why Riley is a navigator in the former episode, while he's a communications officer in the latter.
Kevin's son was featured in the novel Crossover, where he released Captain Scott after Scott stole the USS Yorktown in search of Spock, who had been captured with a group of Unification believers. He released Scott on the promise that he would retrieve Spock and bring back the Yorktown to the museum it was in. He did so because he felt that his father owes Spock for his life after the events of "The Naked Time". It was also noted that Kevin must have had children relatively late in his life, and that his son commanded a Galaxy-class starship.
Kevin Riley was also featured in the Star Trek: The Lost Years series, set between the end of TOS and Star Trek: The Motion Picture. Promoted to Lieutenant Commander, Riley became chief of staff to Admiral Kirk at Starfleet Command. Flashbacks in The Lost Years also revealed Kodos' reign of terror from Riley's perspective, including a memory in which a teenage Kirk hid the then four-year-old Riley from execution.
Riley also appears in the novels The Galactic Whirlpool and Probe. In Probe, set after Star Trek IV: The Voyage Home, he was a protégé of Ambassador Sarek and later became an ambassador himself during negotiations with the Romulans. According to the book Probe, his father was executed when he was very young.
His mirror universe counterpart is depicted in the Star Trek: Mirror Universe novel The Sorrows of Empire as succeeding Spock as captain of the ISS Enterprise after Spock became the ruler of the Terran Empire in 2277. Captain Riley commanded the Enterprise until 2284, when he was succeeded by Saavik.