Jaleel White played Steve Urkel, Myrtle Urkel, and Stefan Urquelle (when Steve accidentally clones himself and have one be permanently Stefan). He even got to be a one-off criminal cousin. All of that, in addition to the transformation chamber, was to allow White some opportunity to not keep up the squeaky Steve voice, which got harder and harder as he grew up. This was also done because White was a talented character actor and impressionist. His Bruce Lee is actually quite good, and reportedly one of his favorite roles. This is partially averted with Urkelbot. While White did provide his voice, it was actually Michael "Boogaloo Shrimp" Chambers who portrayed him.
Reginald VelJohnson also appeared a couple of times as Myrtle's father Big Daddy Urkel.
Darius McCrary is featured singing on several episodes.
In the Bruce Lee episodes, Jaleel White got to show off his magnificent upper body and his love of kung fu. He also got to show his accordion playing, which is actually quite good. Finally, Steve was made into a basketball prodigy despite having no athletic talent anywhere else.
Reginald VelJohnson's singing and dancing.
Jo Marie Payton's singing in a couple of episodes.
Telma Hopkins in the earlier episodes.
Bryton McClure's dancing in some episodes.
Shawn Harrison's tap dancing was made into a plot point where Waldo learned the art in order to play better basketball.
Contest Winner Cameo: The four children picked to be Steve and Laura's children for Carl's nightmare in "Father of the Bride".
The Danza: Maxine Johnson was played by Cherie Johnson.
Dawson Casting: The late Michelle Thomas was in her mid twenties when cast as Myra Monkhouse. She was actually 7-8 years older than the other teen actors.
I Am Not Spock: This series pretty much killed any shot at Jaleel White being taken seriously as an actor, outside of voice acting. This is slightly subverted as White doesn't resent his most famous role and has fond memories of the series. Additionally, he seems to have transcended this if his current roles are any indication.
Jossed: It was widely believed that Jo Marie Payton left the show midway through the final season because she was disgusted that Jaleel White had become the star of the show. It was also believed that she reappeared in the series finale in an uncredited role. In an 2010 interview, however, Payton revealed that she wanted to leave the show for a while in order to do other projects, which she finally did midway through the final season. She also revealed that contrary to popular belief, she didn't appear in the series finale.
Judy was played by a different actress, Valerie Jones, in the pilot.
The actor playing Richie were originally a pair of twins, since he was a baby during the first season.note Joseph and Julius Wright were credited as Joseph Julius Wright. The character went through Soap Opera Rapid Aging Syndrome after this and he was recast with four year old Bryton McClure.
Estelle's husband Fletcher was portrayed by three different actors throughout the show.
Jo Marie Payton, the original star of the show, left halfway through the show's final season and the role of Harriette was recast with Judyann Elder.
Recycled Script: As with all Miller-Boyett sitcoms, the producers weren't shy about recycling ideas from other sitcoms. The Season 2 opener, where Steve burns down the local hangout and it's rebuilt as the cooler "Rachel's Place," was virtually identical to a story involving Arnold's on Happy Days, which several of the writers had worked on.
Typecasting: When hasn't Reginald VelJohnson been cast as a police officer?
The original pilot script apparently had appearances from Balki and Larry, but these scenes were cut and the Required Spinoff Crossover was averted.note On the downside, it meant a lot more fans were left unaware it was even a spinoff to begin with.
Had the show returned for a tenth season, Steve and Laura would have married.