6. Donna Noble - The Runaway Bride
Sometimes the most effective companion arrivals are the most surprising and the least expected. The Doctor certainly wasn't expecting a soon-to-be-married temp from Chiswick to appear in the TARDIS mere seconds after he finished saying farewell to Rose. But appear she did, and Donna Noble was a far cry from a wide-eyed, impressionable young companion. No, she was livid at being yanked out of her wedding so unceremoniously and blamed the Doctor - loudly and repeatedly. The Doctor, in turn, was in no mood to deal with such a difficult woman just moments after permanently saying goodbye to the girl he loved. It seemed impossible that these two would learn to respect each other and get along, but by the end of the episode, the Doctor and Donna parted on good terms. Although Donna wouldn't become a full-time companion until Partners In Crime, The Runaway Bride still served as an excellent introduction for her. In a departure from companions being overwhelmed and impressed, Donna remained grounded. Also, her sudden appearance was actually good for the Doctor; it kept him from getting too upset about losing Rose. By throwing himself into another adventure, the Doctor managed to begin his healing process, and it was all thanks to the best temp in Chiswick.