Styles was a somewhat arrogant man, coming off with an attitude of superiority. He took extreme pride in his assignment as master of the Excelsior, which had been outfitted with an experimental transwarp drive. The night before the Excelsior was to be launched from spacedock, Styles encountered Montgomery Scott, his newly-assigned captain of engineering, telling him that he was "looking forward to breaking some of the Enterprise's speed records."
That same evening, Styles was informed that Admiral James Kirk was attempting to steal the Enterprise, and immediately mobilized the Excelsior crew to stop him. Upon the Enterprise's emergence from the spacedock, Styles contacted Kirk, reminding him that, if he followed through with the illegal action, his career in Starfleet would be over. Kirk ignored him, however, and took the Enterprise to warp. Styles expected to quickly catch up to the Enterprise utilizing the Excelsior's transwarp system, but was unpleasantly surprised to find that Scott, who was Kirk's former chief engineer, had sabotaged the transwarp drive. (Star Trek III: The Search for Spock)
Styles was played by actor James B. Sikking. According to the film's script, "Styles is an officer about Kirk's age. If he's a little stuffy, it's pardonable; he does, after all, have the plum assignment in all of Starfleet."
In the Pocket TOS novel Prime Directive, a younger Lieutenant Styles was the annoying nemesis to Lieutenant Commander Scott (and a discharged Kirk) when he was given temporary command of the damaged USS Enterprise during its refit. He regarded himself as superior to Kirk, stating that, with him in charge, Enterprise would have a "real" captain. However, he lost his position after Kirk was allowed to take the Enterprise to investigate the possibility of foul play; Styles, outraged at this, told a superior officer that he could not do that. The novel also revealed that Kirk and Styles once served together on the USS Farragut, and developed a keen dislike for each other. He picked up his swagger stick from a Klingon that he beat in personal combat. In the novel, Scott, mightily annoyed by the behavior of Styles, broke the stick over his knee.
Styles also made a brief appearance in the Pocket TOS novelization of Star Trek IV: The Voyage Home by Vonda N. McIntyre. Here, still in command of Excelsior, he was ordered by Starfleet Command to intercept and destroy the Whale Probe before it reached Earth. However, he never even made it out of Spacedock before the probe's transmissions rendered his ship and the massive space station around it completely useless.
According to the novel Forged in Fire, Styles was killed in late 2289 at an early peace talk on the planet Korvat between the Klingons and the Federation when a bomb set by a Klingon pirate named Qagh - who became known simply as "the Albino" - detonated in the main chamber. It was at that point that Sulu, Styles' first officer, became captain of the Excelsior.
Styles made an appearance in the comic book series titled The Mirror Universe Saga created by DC Comics. At this point, he was still captain of the Excelsior. At the start of the story, he is trying to retrieve Kirk to answer for disobeying orders, and is captured by James T. Kirk of the mirror universe and placed in a statis chamber.