He was the first Vulcan ambassador to Earth. As such, he was the answer to a crossword puzzle an ensign was trying to solve while forced to live in the catwalk for several days. Captain Archer supplied her with the answer. (ENT: "The Catwalk")
According to the Star Trek Customizable Card Game, Solkar was the Vulcan captain of the T'Plana-Hath who greeted Zefram Cochrane in Star Trek: First Contact. In an unpublished interview with Larry Nemecek, "The Catwalk" writer Mike Sussman believes this as well, citing the wording in Archer's dialog in "Horizon" in which he refers to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."