Who played Mark Greene in 'ER'?

In which TV series is Monica Geller a main character? Who played Phoebe Buffay in 'Friends'? Who played Joey Tribbiani in 'Friends'? In which TV series is Joey Tribbiani a main character? In which TV series is Mark Greene a main character? Who played John Carter in 'ER'? Who played Ray Barone in 'Everybody Loves Raymond'? Who played Debra Barone in 'Everybody Loves Raymond'?