Sybok was Spock's half-brother, a Vulcan who rejected logic and led a quest to find God at the center of the galaxy in 2287.
Sybok was a son of Sarek and the elder half-brother of Spock. Unlike most Vulcans, he rejected the discipline of logic and embraced emotion, believing that this was the true path to self-knowledge. His views led to his banishment from Vulcan.
In Star Trek V: The Final Frontier, Sybok took the leaders of Nimbus III hostage in order to lure a starship to the planet. He had a gift for exposing and easing the inner pain of others, and he used it to gather followers, including many of the Enterprise crew. He took over the Enterprise and drove it through the Great Barrier at the center of the galaxy, seeking the mythical world Sha Ka Ree and the creator he believed lived there. The being they found was a powerful entity imprisoned on the planet, not a god. Realizing his mistake, Sybok sacrificed himself to let the others escape.
Sybok revealed a hidden chapter of Spock's family history, and his mixture of charisma, faith and error made him a tragic figure.