During his tenure in the TARDIS, the Tenth Doctor is known for his energetic, charismatic, and eccentric personality. But it wouldn't be Doctor Who without a dark side. As well as bearing the weight of the Time War, he is faced with countless challenges and losses that push him to his limits.
Of course, this is all part of the package when one is a Time Lord, especially one as danger-prone as the Doctor. As a near-immortal, The Doctor is destined to outlive his friends and loved ones. Still, the Tenth Doctor draws the short straw more often than he deserves from losing his beloved Rose to being imprisoned by the Master.
Losing His Life As John Smith
In one of the Doctor's scariest adventures, he and Martha try to outrun The Family – a group of creatures with the ability to inhabit physical bodies. As they are determined to steal his Time Lord lifespan, he uses the Chameleon Circuit to temporarily become human – erasing his identity in the process. Instead, he becomes teacher John Smith.
John falls in love with nurse Joan Redfern. Eventually, he's faced with the choice of returning to his former life or letting the Family run unchecked. In choosing the former, he loses an entire identity – and an entire future. While John Smith may not have been real, the grief and emotions are.
Madam De Pompadour's Death
The Doctor only knows Madame de Pompadour for a short time, but she knows him for nearly her entire life. Thanks to a fireplace that connects 18th-century France to a 51st-century spaceship, their paths occasionally cross throughout her timeline and the pair develop a strong bond.
Despite doing everything he can to save her from the clockwork creatures determined to take her brain, time is not on the Doctor's side. Madame de Pompadour passes at a young age before she can join him in the TARDIS, leaving her "lonely angel" a heartbreaking letter. The Doctor is devastated – the idea of what could have been made this a tough loss to process.
Spending A Year As The Master's Pet
Theoretically, the Doctor and the Master should've grown closer in the wake of the Time War. However, old habits die hard – even when you are the last remaining Time Lords in the entire universe – and the Master ends up imprisoning the Doctor and using de-aging technology to visibly age the Doctor by 100 years.
As if this isn't bad enough, the Doctor is kept as the Master's pet for a year, living in a tent on his ship. The Master then goes on to age him further until he shows his full age (with some questionable CGI). It would be demeaning and unbearable for anyone, but especially your old friend and only other sole survivor from your homeworld.
Adelaide's Suicide
The events of "Waters of Mars" possibly show the Doctor at his very darkest. After successfully changing a fixed point in time (and saving Adelaide's life in the process), he believes himself to be the Time Lord Victorious. He thinks he has the power to say who lives and dies in his hands.
Adelaide emphatically believes that he is wrong – and takes her own life to restore balance to the universe. It's a shocking scene for the audience and Doctor alike. He's overcome with horror at his actions, falling deep into the Doctor's default setting: extreme guilt. It's his fault but sends him on a spiral that ultimately ends with the Tenth Doctor's death.
River Song's Sacrifice
Another cause of the right person, mismatched timelines is the Doctor and River Song. The first time the Doctor meets his future wife also happens to be the day of her death, when she sacrifices herself to save the souls uploaded to the Library's computer.
The Doctor feels guilty for every death that happens on his behalf, but this one is more complicated than most. He doesn't have the time to get attached to River – yet knows that one day he'll care for her so much that he tells her his name. It's a complicated thing, to know he'll have to experience their entire future relationship knowing exactly how it ends.
Leaving Rose With His Clone
The Doctor doesn't just lose Rose once, but twice. In "Journey's End", he's saddled with a half-human, half-Time Lord clone of himself who he considers dangerous, as he was born in the heat of battle. There's one positive: as he's half-human, this version of himself won't regenerate and can live a human life.
And so the Doctor decides to leave him with Rose in the parallel world. Rose and the Doctor could never be a happy, human-ish couple – but she and his clone can. Considering how much he missed her the first time, saying goodbye for good is devastating – even if he brought it upon himself for purely selfless reasons.
The Return Of The Time Lords
The Doctor's guilt around the Time War is a complex issue. While he's distraught at killing his race, he also knows that the Time Lords were growing too strong – and too vengeful – and would ultimately have ended up destroying time itself.
So, when the Master helps them return in "The End of Time", he's faced with repeating history all over again. Reliving his hardest choice ever is a grueling task. Especially when it inadvertently leads to his 'death' and regeneration.
Taking Donna's Memories
The Doctor and Donna are arguably one of the best TARDIS teams the show has ever seen. Unlike his previous pairings with Rose and Martha, there's absolutely zero romantic chemistry between them. Instead, Donna is the Doctor's best friend, challenging and entertaining him in equal measure.
That's until he's forced to say goodbye to her forever. Having absorbed some Time Lord DNA, Donna is overwhelmed with knowledge and the Doctor must wipe her memory to save her life. This is a goodbye that happens far too soon – and the fact Donna can't miss him the way he misses her makes it even more painful.
Watching The Master Die
The Doctor and the Master's rivalry is infamous. However, even when the Master keeps the Doctor as his pet and unleashes the Toclafane on earth, the Doctor is willing to forgive him because they're the last two Time Lords left.
But the Master won't give him the pleasure. Refusing to regenerate, he dies in the Doctor's arms. Of all the deaths during the Tenth Doctor's life, his reaction to this is the most gut-wrenching as he realizes that he is, once again, completely alone.
Losing Rose
The Tenth Doctor and Rose are the closest the Doctor has ever come to a romantic relationship with a companion. They dance around their feelings during Rose's time on the TARDIS, with the truth only being said out loud when Rose is trapped in a parallel universe in the season two finale "Doomsday".
The loss devastates the Doctor. Not only does he have to say goodbye, but his connection is broken just as he's about to finally tell Rose "I love you." This remains one of Doctor Who's most devastating companion exits – and it takes the Doctor longer to recover from than any other, with his feelings stretching to his next regeneration.