The BBC has officially announced that actor David Tennant has been signed to play Dr. Who in the next season of the recently revived TV series. Actor Christopher Eccleston has played the good Dr. in the first new batch of shows, but almost immediately announced his retirement thereafter.
Unlike Eccleston’s first show, Tennant’s first episode will reportedly feature the traditional regeneration scene that allows for different actors to play the Timelord. From this I assume Eccleston is amendable to returning for a portion of that first chapter.