Who played Richie Cunningham in 'Happy Days'?

In which TV series is Klinger a main character? Who played Fred Sanford in 'Sanford and Son'? Who played Arthur "Fonzie" Fonzarelli in 'Happy Days'? In which TV series is Arthur "Fonzie" Fonzarelli a main character? In which TV series is Richie Cunningham a main character? Who played Charles Ingalls in 'Little House on the Prairie'? In which TV series is Charles Ingalls a main character? Who played Laura Ingalls in 'Little House on the Prairie'?