In which TV series is Turk a main character?

Who played Gil Grissom in 'CSI: Crime Scene Investigation'? In which TV series is Gil Grissom a main character? Who played J.D. in 'Scrubs'? Who played Turk in 'Scrubs'? Who played Dr. Perry Cox in 'Scrubs'? In which TV series is Dr. Perry Cox a main character? Who played Sydney Bristow in 'Alias'? In which TV series is Sydney Bristow a main character?