Who played Dwight Schrute in 'The Office'?

Who played Derek Shepherd in 'Grey's Anatomy'? Who played Cristina Yang in 'Grey's Anatomy'? In which TV series is Cristina Yang a main character? Who played Miranda Bailey in 'Grey's Anatomy'? In which TV series is Dwight Schrute a main character? Who played Pam Beesly in 'The Office'? In which TV series is Pam Beesly a main character? Who played Andy Bernard in 'The Office'?