In which TV series is Monica Geller a main character?

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'? Who played Phoebe Buffay in 'Friends'? Who played Joey Tribbiani in 'Friends'? In which TV series is Joey Tribbiani a main character? Who played Mark Greene in 'ER'?