Steve Urkel was only supposed to appear once, but the audience's response was so overwhelmingly positive that the producers decided to make him a regular character. He became the most popular character of the show, so much that merchandise based on him was made, which included a talking doll, trading cards, posters, books, lunch boxes, T-shirts, and a limited-edition cereal called "Urkel-O's".
By the time the show ended in 1998, 22-year-old Jaleel White had grown sick of the role of Urkel. In 1999, he said in an interview, "If you ever see me do that character again, take me out and put a bullet in my head, and put me out of my misery." In a 2011 interview, he said, "It's one of those things that very unfortunate how quotes are taken out of context. I remember that interview very vividly. I loved playing those characters. But the fact is that I was maturing. Honestly, I was retarding my growth as a man to maintain the authenticity to what I thought that character should be."
Valerie Jones played Judy, the youngest Winslow child, in the pilot, but Jaimee Foxworth replaced her. Judy had little screen time. When Foxworth requested a salary increase, producers wrote her off the series. Later episodes revised the show's history, so Judy never existed.
Jaleel White went through puberty as the series progressed. He shaved daily and avoided weightlifting. As White got older, Steve Urkel's clothing got baggier to hide his growing muscles.
The show lasted one year longer than its parent series, Perfect Strangers (1986), in which Harriette Winslow was an elevator operator.