Who played Danny Zuko in 'Grease'?

In which film is Maria von Trapp a character? Who played Randle McMurphy in 'One Flew Over the Cuckoo's Nest'? Who played Colonel Nathan Jessup in 'A Few Good Men'? In which film is Colonel Nathan Jessup a character? In which film is Danny Zuko a character? Who played Sandy Olsson in 'Grease'? In which film is Sandy Olsson a character? Who played Tony Manero in 'Saturday Night Fever'?