Solkar of Vulcan was a male Vulcan of the 21st century and 22nd century. He was the father of Skon, grandfather of Sarek, and great-grandfather of Sybok and Spock. (ENT: "The Catwalk"; Star Trek III: The Search for Spock)
Solkar was the first Vulcan ambassador to Earth and, as such, was the answer to a crossword puzzle which a female crewmember was trying to solve while forced to live in Enterprise NX-01's catwalk for several days. Captain Archer supplied her with the answer. (ENT: "The Catwalk")
According to the Star Trek Customizable Card Game and Stellar Cartography: The Starfleet Reference Library ("Stellar Cartography", p. 25), Solkar was the Vulcan captain of the T'Plana-Hath who greets Zefram Cochrane in Star Trek: First Contact.
According to Who's Who in Star Trek 2, Solkar was Sarek's mother, rather than his grandfather. This is due to the ambiguity of the "child of Skon, child of Solkar" line.
In an unpublished interview with Larry Nemecek, "The Catwalk" writer Mike Sussman said that he intended Spock's grandfather Solkar referenced in that episode to be the unnamed Vulcan captain of the T'Plana-Hath from First Contact. Sussman later strengthened the case for Solkar's appearance in the film in an exchange he wrote between T'Pol and Archer for "Horizon", for which Sussman performed an uncredited rewrite. In that episode, after watching Frankenstein (1931) on the crew's movie night, T'Pol noted that the reaction of the villagers to the monster "was similar to the reception Vulcans received after landing on Earth." Archer replies, "I don’t recall anyone greeting the Vulcan ambassador with torches and pitchforks." (Information provided by Larry Nemecek)