Vicki was the first new regular character to join the show since it began. After dumping wet blanket granddaughter Susan, the Doctor immediately replaced her with surrogate granddaughter Vicki, an orphan from the 25th century. He traded up.
Vicki was highly intelligent, which was the norm in her time thanks to futuristic teaching techniques; something she never hesitated to tease 20th century teachers Ian and Barbara about. She was smart, but not necessarily perceptive. When the Doctor found her, in The Rescue, she was one of only two survivors of a spaceship crash, along with a man named Bennett. While they await a rescue ship, Vicki is randomly menaced by a creature named Koquillion.
Spoilers! In a twist anticipating Scooby-Doo by several years, Koquillion is Bennett in a mask. This never occurs to Vicki, despite the fact that she never sees the two of them together, and that Bennett always withdraws to his room just before Koquillion appears. To give Vicki the benefit of the doubt, though, this is classic Doctor Who, and she can be forgiven for not being able to tell the difference between an actual alien head and a cheap rubber mask.
Mystery sleuthing skills aside, Vicki was adventurous and brave. When the foursome relaxed in an ancient Roman villa for a month, Vicki complained about nothing exciting happening (until they met Nero and he burned Rome down, which she totally dug).
When the crew landed in Palestine during the Crusades, the Doctor convinced her to disguise herself as a boy, for her own safety. Here she is, disguised as "Victor", along with Ian, the Doctor, and King Richard.
King Richard suspected nothing, because in ancient times the idea of a girl wearing trousers or a tunic was so inconceivable it was a fool-proof disguise, even though she clearly has boobs.
Here she is in the TARDIS, reading over Ian's shoulder. Don't you hate that? Leave him alone, Vicki, he just wants to read about monsters from outer space in peace.
Here she is in Ian and Barbara's final story, The Chase. And in another example of her fine observational skills, this giant walking fungoid monster is SNEAKING UP ON HER! Pay attention, Vicki! I know it looks like the set of H.R. Pufnstuf, but you're in real danger here!
Ian and Barbara were replaced by space pilot Steven Taylor. Here's the new TARDIS crew in the story Galaxy 4, being menaced by giant upside-down shower drain stoppers.
Fab dress, don't you think? Vicki matured a great deal during her travels with the Doctor, and I'm not just talking about her boobs. She took her leave in the next story, The Myth Makers, in which the TARDIS trio landed outside Troy, during the war. (Because really, if you're a time traveler, when else are you going to go to Troy?)
Here she is meeting King Priam. Provincial Priam thought the name Vicki was weird, so he renamed her Cressida. (Do you see where this is going?) Vicki promptly falls in love with Priam's son Troilus, and leaves the TARDIS to be with him and fulfill her destiny. For some reason the Doctor did not point out to her that this would probably not turn out well.
Still, if you ignore the whole definition-of-a-faithless-woman thing, going from future space orphan to famous literary figure isn't too bad a deal. Unless Chaucer was right, and she later got leprosy. Uh...maybe we should just leave off at the end of The Myth Makers, when Vicki's happy with Troilus, and try not to think about what might have come later...