James T. Kirk/Starfleet career/USS Enterprise-A/Sybok and Sha Ka Ree

In 2287, after a brief shakedown cruise proved the Enterprise-A not quite to be as fully spaceworthy as it had initially seemed to be, Kirk vacationed in Yosemite National Park with Spock and McCoy, while Montgomery Scott attended to the technical problems. The respite was interrupted after Spock's half-brother, Sybok, raised a small force called the Galactic Army of Light to take over the planet Nimbus III and captured the Federation, Klingon and Romulan representatives. 
Kirk and the Enterprise-A responded, as did a Klingon Bird-of-Prey commanded by Klaa, who took on the rescue mission as an opportunity to take on Kirk, as he believed defeating Kirk would make him the greatest warrior in the galaxy. 
Following a failed assault on Paradise City, Sybok captured the crew of the Enterprise-A and took over the ship. After most of Kirk's crew fell under Sybok's influence and joined in his quest to meet "God" by taking the starship through the Great Barrier to the legendary Sha Ka Ree. En route, Sybok offered Kirk the chance to "ease his pain," as he had seemingly demonstrated on Spock and McCoy. But Kirk rejected the offer angrily, insisting, "I don't want my pain taken away; I NEED my pain!!!" 
Later, the entity they encountered proved to be a malevolent force, imprisoned and looking for release. Sybok joined the entity in combat, sacrificing himself and permitting the Enterprise-A to escape. ()