In which TV series is Dr. Perry Cox a main character?

Who played J.D. in 'Scrubs'? Who played Turk in 'Scrubs'? In which TV series is Turk a main character? Who played Dr. Perry Cox in 'Scrubs'? Who played Sydney Bristow in 'Alias'? In which TV series is Sydney Bristow a main character? Who played Clark Kent in 'Smallville'? In which TV series is Clark Kent a main character?