Tina Fey, who served as head writer and Weekend Update anchor on Saturday Night Live from 2000-2006, stars on 30 Rock as main character Liz Lemon. She's also the show's creator, producer, and often writes many of the episodes.
Tracy Morgan, who starred on SNL from 1996-2003, stars as actor Tracy Jordan on 30 Rock, in a role that's very much based on himself. In this season 1 clip, he releases to the world his hit single "Werewolf Bar Mitzvah":
Rachel Dratch left SNL with Tina Fey in 2006 to star on 30 Rock as the character of Jenna. The part was eventually recast with Jane Krakowski playing the part, but Rachel appeared throughout the first season as a different random character in each episode. In the clip below she plays a cat wrangler:
Chris Parnell plays NBC's in-house doctor Dr. Leo Spaceman (pronounced Spa CHE man). He has appeared on all 7 seasons of 30 Rock, and is one of our personal favorite characters. Here is a montage of some of his funniest medical moments: