Dr. John Carter, portrayed by Noah Wyle, was one of the main characters in ER. Wyle decided to leave the show as a regular character at the end of season 11, despite offers to stay. Carter was then written out of the show by moving to Africa and marrying his fiance, Makemba Likasu.
Noah Wyle agreed to make two four-episode appearances in Seasons 12 and 13. While he did so in Season 12, his Season 13 episodes were pushed back to season 14. Because of the WGA Strike, ER was renewed for a 15th season (it was originally suposed to end after Season 14), during which Wyle appeared in a few episodes as part of the show’s plan to bring back former regulars.