series feature major or supporting characters whose love of Star Trek affects the storyline of the series. "The Replacement", a Season 5 episode of Buffy the Vampire Slayer, features two versions of the character Xander, a huge Star Trek fan, which is a simultaneous tribute to the original series episode "The Enemy Within", in which there are two Captain Kirks. In crossover casting, two other television series have cast actors from Star Trek in series in which other characters are Star Trek fans who frequently refer to Trek moments or cite Trek storylines. The character Hiro Nakamura on NBC's Heroes likes to describe his ability to teleport as "like Star Trek", and has often performed Mr. Spock's Vulcan salute. His father is played by George Takei, who played Hikaru Sulu on the original series. Additionally, Nichelle Nichols, who played Nyota Uhura on the original series also appears on the series. Over a dozen actors from various Star Trek series have made guest appearances on one or the other of the Stargate series. In those series, Colonel Jack O'Neill makes unsuccessful pitches to name new space vessels after the Enterprise, and also gives the Vulcan salute in tribute to Trek. In an earlier episode of Stargate: SG-1, O'Neill travels back in time to the 1960s and during an interrogation by an Air Force officer he refers to himself as "James T. Kirk, captain of the federation starship Enterprise". Another Trek reference is made when a character questions whether or not another team member can be "beamed up". The response is "What am I, Scotty"? Later on the series, advanced alien technology allows team members to "beam" up and down in manner similar to that seen on Star Trek. In the Cold War submarine film Crimson Tide (1995), in a moment of crisis, the USS Alabamas executive officer (played by Denzel Washington) gives a pep talk to his young radioman, urging him to repair the ship's radio by referring to Captain Kirk telling Scotty they need "more power". The Trek fandom of Noel, a recurring character on the sitcom Frasier, plays a role in several episodes, including "Star Mitzvah", in which he deceives Frasier into believing a speech is written in Hebrew when it is really in the Klingon language. The main characters from the sitcom The Big Bang Theory, especially Sheldon Cooper, make various references to and are huge fans of