Trey was born in Conifer, Colorado, on October 19, 1969 to Randy Parker, a geologist, and Sharon Parker, an insurance broker. He has an older sister, Shelley Parker. He met Matt Stone (co-creator of South Park (1997)) while attending the University of Colorado in Boulder, where he had a double major of music and Japanese. While at UCB he wrote, directed and starred in Alferd Packer: The Musical (1993) (aka "Cannibal: The Musical!") based on a true episode in Colorado's history. After graduation from UCB (rumors that he didn't due to skipping classes to work on the movie are false), he and Stone were asked by then-FoxLab executive Brian Graden to create an animated Christmas card for his friends and family. The now infamous short, titled The Spirit of Christmas (1995), led to South Park (1997).