Lady Christina de Souza

Lady Christina de Souza is a fictional character played by Michelle Ryan in the long-running British science fiction television series Doctor Who. She is a one-off companion of the Tenth Doctor (David Tennant) appearing in the episode "Planet of the Dead". In place of an ongoing companion for David Tennant's final five episodes, Lady Christina follows Jackson Lake (David Morrissey) as the guest character assisting the Tenth Doctor.

Conception
"[I]nternational woman of mystery - and part-time jewel thief" Lady Christina de Souza has "a mysterious past" according to writer Russell T Davies. Davies goes on to state that Lady Christina has "a huge impact on the Doctor" when they meet in "Planet of the Dead". Lady Christina "loves extremes" according to actress Michelle Ryan whom identifies with her character in this regard. Ryan asserts that Lady Christina is "an adrenaline junkie" and "is very sassy and charismatic" and that she is "in it purely for the thrill of it and for herself and for the adventure [...] always chasing the next high". Ryan describes Lady Christina as a "really fun, really cool character" and notes that there is a "chemistry between the Doctor and Christina".

Character history
Lady Christina is a bored aristocrat who takes to burglary for the excitement it provides. Pursued by the police after stealing a priceless Medieval drinking cup from the International Gallery in London, Lady Christina boards a bus moments before it unexpectedly enters a wormhole and is transported to the alien planet San Helios. She teams up with fellow passenger the Doctor to fend off alien predators and find a way back to Earth. Ryan asserts the adventure provides "a real journey for Christina because [...] the Doctor [...] makes her realise that she can use her a lot of her skills as being part of a team as oppose to just being off for herself".

Casting
Michelle Ryan's casting as Lady Christina de Souza was confirmed by the BBC on 23 January 2009. Ryan stated that she is "a huge fan of Doctor Who and [was] very excited to be joining David Tennant and the Doctor Who team." Davies commented that "Michelle is one of the most sought after young actors in the country" and that they were "delighted to announce that she [would] be joining the team." Ryan described her casting as a "real honour", noting that she "love[s] the character". Ryan's casting in "Planet of the Dead", combined with her previous working history with incoming Executive Producer Steven Moffat, prompted speculation that she might return to Doctor Who as a full-time companion to the incoming Eleventh Doctor (Matt Smith). Ryan herself has ruled out a return, however, stating that she regards "Christina as someone who is around for this one-time adventure" and asserting that she is reluctant to become a regular on Doctor Who because she is "a commitment-phobe." Reportedly, Ryan auditioned to replace Billie Piper in the companion role when her character, Rose Tyler, left in 2006, but she was unsuccessful.