Who played Latka Gravas in 'Taxi'?

Who played Jack Tripper in 'Three's Company'? Who played Chrissy Snow in 'Three's Company'? In which TV series is Chrissy Snow a main character? Who played Mork in 'Mork & Mindy'? In which TV series is Latka Gravas a main character? Who played Louie De Palma in 'Taxi'? In which TV series is Louie De Palma a main character? Who played J.R. Ewing in 'Dallas'?