In pictures: Doctor Who's companions

Catherine Tate follows in a long line of actors who have travelled with the Doctor. Secretary Polly (Anneke Wills) and seaman Ben (Michael Craze) were early sidekicks.

Jo Grant (Katy Manning) often wandered into danger - needing the third Doctor to help her out.

Sarah Jane Smith (Elisabeth Sladen) travelled with the third and fourth Doctors and returned most recently in 2006. She also has her own children's spin-off series.

Leela (Louise Jameson) was a tribal warrior who joined up with Tom Baker's Doctor in the adventure The Face of Evil.

Adric (Matthew Waterhouse), air hostess Tegan (Janet Fielding) and Nyssa (Sarah Sutton) with the fifth Doctor Peter Davison.

Nicola Bryant played Peri, who joined Davison as an 18-year-old American botany student, and went on to travel with the sixth Doctor Colin Baker (pictured).

Actress Bonnie Langford played Mel, who travelled with both Colin Baker and Sylvester McCoy (pictured).

Rose Tyler (Billie Piper) joined the ninth Doctor (Christopher Eccleston) in 2005. He regenerated into David Tennant, and Rose stayed on until she got trapped in a parallel universe.

Martha Jones, played by Freema Agyeman, joined the 10th Doctor in the 2007 series. She will next appear in spin-off show Torchwood.

Catherine Tate will become David Tennant's assistant Donna in the next series of Doctor Who. She appeared in the 2006 Christmas special as a bride escaping her wedding.