In which TV series is Chrissy Snow a main character?

Who played Vinnie Barbarino in 'Welcome Back, Kotter'? In which TV series is Vinnie Barbarino a main character? Who played Jack Tripper in 'Three's Company'? Who played Chrissy Snow in 'Three's Company'? Who played Mork in 'Mork & Mindy'? Who played Latka Gravas in 'Taxi'? In which TV series is Latka Gravas a main character? Who played Louie De Palma in 'Taxi'?