Originally, Zack and Slater were written as bitter rivals for Kelly's romantic affections. Off-screen, Mario Lopez and Mark-Paul Gosselaar were (and continue to be) very close friends. The writers, sensing their obvious chemistry, had the characters re-written as best friends, and they remained that way for the rest of the show.
Although Kelly was Zack's girlfriend for the show, Lark Voorhies was Mark-Paul Gosselaar's real-life girlfriend for three years, including Saved by the Bell: Hawaiian Style (1992), according to several interviews by Gosselaar.
At its height, the show had more teenaged viewers on Saturday mornings than The Cosby Show (1984), the number one show on television at the time, did at primetime.
Elizabeth Berkley originally auditioned for the role of Kelly Kapowski. Although she didn't receive the part of Kelly, producers liked her so much they wrote the part of Jessie Spano for her.