I noticed long ago the similarity in the names of the two sitcom stars described below. A quick trip to the Internet Movie Database revealed that the two have yet to appear on the same show together, which surprised me somewhat. Hey, I guess it avoids confusion! Anyway, good luck with today's Brain Game:

What sitcom star of the 1970s becomes
a sitcom star of the 1980s-90s if you
add the letters "ST" to his name?
 

See the answer here.

Answer: JOHN AMOS (James Evans on Good Times) becomes JOHN STAMOS (Uncle Jesse on Full House) when you add the "ST".