Who played Steve Urkel in 'Family Matters'?

Who played Kelly Kapowski in 'Saved by the Bell'? In which TV series is Kelly Kapowski a main character? Who played Screech Powers in 'Saved by the Bell'? In which TV series is Screech Powers a main character? In which TV series is Steve Urkel a main character? Who played Sam Beckett in 'Quantum Leap'? In which TV series is Mitch Buchannon a main character? Who played C.J. Parker in 'Baywatch'?