Elliot Langley is a researcher at Lawrence Livermore Labs. Dan contacts Langley in "The Year of the Rabbit" to learn about tachyons, and subsequently speaks with him on the phone in the past. Later in "The Legend of Dylan McCleen", Langley meets with Dan at the Register to further discuss what Dan explains is research for a science fiction novel.
In "Winterland", Langley meets with Dan and warns him not to tell anyone about the work he's doing for the "novel." Langley says he had to give up his work with crystal quartz because, using the PATRIOT Act, "men with guns always want to control ideas."
Later, Dan goes back to the seventies, where he follows a group of young hippies associated with his charge, Abbie. One of those hippies also speaks of the time precision qualities of crystal quartz (and wears a piece of quartz on a string around his neck), and of tachyons (tachyons are also associated with Langley's research). Dan reveals to the group that he is a time traveler from 2007.
In "The Hanged Man", Dan inadvertently changes his own life. Having changed it back by the end of the episode, he meets Langley at the labs, who denies knowing him and has him sent away.
In "Perfidia", Jack begins to seek answers from Langley. He approaches him in a parking lot, but Langley continues to deny any knowledge of Dan and his powers. He continues this when Jack sits in on one of his lectures and asks him about time travel in front of the whole audience.
Later, Langley turns up at the Register looking for Dan. They speak whilst in the elevator. Langley says that he will forever deny knowledge of Dan's gift because some people would do horrible things to get something in their past altered. He explains that Dan has a gift and he has to use it because he is the only traveller left. Dan denys this, but does not divulge that the other person he speaks of is his ex-fiance, Livia Beale.