Barbara Wright (Jacqueline Hill)
Barbara was a teacher at Coal Hill School when she first encountered the Doctor, through his granddaughter, Susan. With colleague Ian Chesterton she went to investigate the strange girl's home, and stumbled into the TARDIS.
Her knowledge of history proved useful, as her travels with the Doctor included visits to 15th century South America, France in 1793, Rome during Nero's reign, and a lengthy journey in the company of Marco Polo.
The Doctor's many attempts to take Ian and Barbara back to contemporary Earth were unsuccessful: it was a Dalek time machine that provided them with the opportunity to finally return home.