In which TV series is Niles Crane a main character?

Who played Dana Scully in 'The X-Files'? In which TV series is Dana Scully a main character? Who played Frasier Crane in 'Frasier'? Who played Niles Crane in 'Frasier'? Who played Daphne Moon in 'Frasier'? Who played Khadijah James in 'Living Single'? In which TV series is Khadijah James a main character? Who played Monica Geller in 'Friends'?