The Tenth Doctor's (David Tennant) third companion Donna Noble (Catherine Tate) was one of the fiercest and funniest characters on Doctor Who. Donna Noble outwitted Daleks, solved mysteries with Agatha Christie, and saved the entire universe on multiple occasions. Although Donna was only a companion for one season, she will be forever be remembered in Doctor Who as the most important woman in the whole of creation. Tragically, Donna never knew how important she was.

In Doctor Who season 4, episode 13, “Journey’s End” Donna Noble absorbed the Doctor’s regeneration energy and gained the knowledge of the Time Lords. She used these skills to stop Davros from destroying the universe and returned everyone safely home. Afterward, Donna's human mind was overwhelmed so the Doctor erased all of her memories of their adventures in order to save her life. From then on if she ever remembered anything about the Doctor her mind would burn and she would die. She then lived out a normal life, never to travel the universe again. Donna's exit has gone down in Doctor Who history as one of the most tragic character departures, almost as tragic as The Tenth Doctor's ending.

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What separated Donna’s departure as particularly tragic on a show full of heartbreaking character exits is that she didn’t choose her fate it was chosen for her. Every other companion who traveled with the Tenth Doctor got some say in their fate, except Donna. Rose Tyler chose to return to the alternate dimension with her clone of the Doctor, Martha Jones left to join UNIT, but Donna begged and pleaded not to be returned to her former state. the Doctor chose to erase Donna's memory so she lost her identity, her best friend, and her past and future with the Doctor.

Catherine Tate as Donna Noble in Doctor Who

Audiences witnessed Donna’s gradual character growth throughout her time with the Doctor, which made it even more painful when that development was erased. Donna was so beloved that there are rumors Catherine Tate may return as Donna in Doctor Who. In her first appearance in Doctor Who series three, episode one, "The Runaway Bride" Donna was rude, insecure, and desperate for love. However after she reunited with the Doctor in series four, she demonstrated her bravery by standing up to the Sontarans, and her kindness by standing up for the Ood. By the time Donna absorbed the Doctor's regeneration energy she had overcome her insecurities and was at her most confident. In her last fully conscious moments she tells the Doctor “Please don’t make me go back.” This implied she would rather die than lose her confidence. Even though the Doctor saved her life by wiping her memory, he took away Donna’s developed sense of self-worth.

Donna's exit was also extremely tragic because it devastated the Tenth Doctor until his last moments.  Donna implied she would rather die than live without her memories, but the Doctor knew her life was precious regardless of her memories and refused to let her die. Although the Doctor did the right thing, he suffered tremendous guilt regardless and once again found himself alone. Throughout the rest of Tennant's run, audiences saw how that decision haunted him. In the 2009 special "The Waters of Mars" audiences watched as the Doctor played God with the matters of the universe because he was tired of making difficult choices that hurt his friends, even if he made those choices for good reasons.

Donna’s fate is tragic and unfair, but also understandable. Her fate demonstrated how Russel T. Davies' first era of Doctor Who grappled with difficult choices that resulted in tragic consequences, and how doing the right thing is not always rewarded. The tragedy of Donna Noble will forever go down in Doctor Who history as one of the most devastating decisions the Doctor ever made.

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The Doctor Who special "Legend of the Sea Devils" premieres April 27 on BBC