5. Catherine Tate – Donna Noble
The show’s most enduring comic presence took the unexpected form of Catherine Tate, who played bolshy bride-to-be Donna Noble in 2006’s The Runaway Bride before hopping aboard the TARDIS full time for Series Four in 2008. When she first met David Tennant’s Doctor, Donna wasn’t the most obvious choice for a companion. Like Matt Lucas she arrived as a festive guest star and the story of her wedding being interrupted by the fearsome, spider-like Racnoss race seemed to bring her journey full circle.
However Tate crossed paths with the Time Lord again in oddball fat reduction tale Partners In Crime, leading to a close – yet strictly platonic! – relationship. Thanks to Tate’s engaging performance, Donna developed convincingly from strong-willed human to all-powerful hybrid after she absorbed the Doctor’s universal knowledge. To protect her sanity he erased her mind, leaving them strangers, but she had one last hurrah in Tenth swansong and Master-fest The End Of Time. Tennant and Tate’s friendship lasted beyond time and space and they reprised their roles for a series of audio adventures in 2016.