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")
Sarek followed in Solkar's footsteps and became an ambassador. Sarek wanted his son Spock to do the same, but Spock chose a career in Starfleet instead. (TOS: "Journey to Babel") He eventually became an ambassador himself, after serving in Starfleet. (TNG: "Unification I")
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In an unpublished interview with Larry Nemecek, "The Catwalk" writer Mike Sussman stated that he believes this as well, citing the wording in Archer's dialogue in "Horizon", in which he refers to Cochrane's first contact and says, loosely, "I don't remember anyone going after the Vulcan ambassador with pitchforks and torches when they first landed." (Information provided by Larry Nemecek)