The Doctor's original companion. The definite article, you might say. And, to all intents and purposes, Carole Ann Ford really is the one who started it all. Introduced as the Doctor's plucky granddaughter in the very first episode, An Unearthly Child, Susan Foreman was the precedent on which all future companions would be set. At least, the ones who spent all the their screaming and asking the important - *ahem* - plot-summerising questions such as, "What is that?" "Where are we?" "Who am I?!". Thank God for Sarah Jane Smith. Not that Susan's tenure aboard the TARDIS was completely irrelevant, of course (she did get to trip over in one episode), but her real life alter ego does blame her character's lack of dramatic range for destroying her subsequent acting career. In fact, she went as far as to say that she was lulled into accepting the role under false pretences after being promised that Susan would be an "Avengers-type girl" harbouring "telepathic powers". Suffice to say, she wasn't.