Serving as Chief Science Officer, Spock was to become one of the most popular characters in the series, and probably the closest and greatest friend of Kirks.

Spock was the first Vulcan to ever enlist in the Federation Starfleet. He began to distinguish himself, using his power of logic, aboard the U.S.S. Enterprise under the command of Captain Christopher Pike. Spock served with Pike for approximately 11 years and 4 months. He then served on the Enterprise under the command of Captain Kirk.

Spock retired from Starfleet at the end of Kirk's five year mission on the Enterprise. He returned to Vulcan where he pursued the Kolinahr discipline. This discipline was intended to purge all remaining emotion and, although Spock completed the training, he failed to achieve Kolinahr because his emotions were stirred in 2271 by the V'ger entity.
After this, Spock remained with Starfleet until the Enterprise was assigned as a training vessel to Starfleet Academy, when he was promoted to captain of the starship.

Spock was killed in 2285 while saving the Enterprise from the detonation of the Genesis device by Khan Noonien Singh. Following the naval tradition, his body was consigned to space, but unknown to anyone at the time, his casket landed on the Genesis planet.
Prior to his death, and following Vulcan tradition, Spock had mind melded with a close friend and given them his 'katra'. That friend was Dr. Leonard H. McCoy (the katra is the Vulcan concept of a soul, or living spirit) and it was McCoy's duty to return Spock's katra to Vulcan.
After the discovery of the regenerated Spock on the Genesis planet, the fal-tor-pan (re-fusion) process was carried out on Mount Seleya, Vulcan, by the high priestess T'Lar. Spock underwent several months of re-education in the Vulcan ways and, heeding the concerns of his human mother, Amanda, that he regain knowledge of his human heritage as well, he returned to Earth with his shipmates to face the charges that occurred stemming from Kirk's violation of Starfleet regulations in his own rescue.

In later years, Spock became more of a diplomat that scientist. At the request of his father, Ambassador Sarek, Spock served as Federation special envoy to the Klingon government in 2293. This paved the way for the Khitomer peace accords with Chancellor Azetbur.

In 2368, Spock secretly travelled to Romulus where he tried to further the cause of the Vulcan - Romulan re-unification. Spock's contact on Romulus was Senator Pardek who, it was later discovered, was an agent of the conservative Romulan government seeking to use Spock's initiative to cover an attempted invasion of Vulcan.

Spock continued to work in the Romulan underground and in 2369, he helped to arrange the defection of Romulan Vice-Proconsul M'ret. Spock believed that this would establish an escape route for other Romulan dissidents fearing for their lives.

Spock's father, Sarek, died in 2368. But Spock had one more unexpected encounter with his father not very long after this. Jean-Luc Picard made contact with Spock on Romulus and told him that Sarek, before his death, had mind melded with him. He then allowed Spock to mind meld with him and it was then that Spock finally came to know of his father's love for him.