Rory Williams was originally determined to outrun the Weeping Angels on Doctor Who Season 7 Episode 5, "The Angels Take Manhattan" so he wouldn't spend the rest of his life without Amy.

While he was running he realized the only way out was to die, again. Standing on the top of the building he asked Amy to push him off sure that he'll come back to life. (He'd done it before.)

She couldn't do it, so she got up on the ledge with him, and they jumped together.

The Doctor is always willing to die for humanity, but some humans are just not willing to let him. Included on that list is River Song.

When the audience first meets her on Doctor Who Season 4 Episode 8, "Silence in the Library," we learn that she has a whole future with the Doctor and she's not going to give that up.

So she takes the Doctor's place and saves him. But that's not the end of the story. Since the Doctor knows that this is going to happen he figures he found a way to save her life, which he did...with his sonic screwdriver. River Song's mind now lives in a computer filled with every book ever written.

After being stuck in his confession dial for four and a half billion years, the Doctor uses an extraction chamber on Gallifrey to save Clara from her death on Trap Street. But the action comes at a cost.

Clara's pulse should have started again when they left Gallifrey, but it hasn't. That means that time isn't healing and her death is a fixed point that the universe counts on happening. The entire scenario is further complicated by the realization that Clara and the Doctor, together, make up the creature known as The Hybrid. And together, they threaten all of time and space. Using the sonic glasses Clara reverses the polarity on a neural blocker, which will cause one of them to lose their memory of the other.

Ultimately, the Doctor forgets Clara, but using the stolen Tardis she's able to bring him to Nevada, return his Tardis to him, and say goodbye in the guise of a diner waitress.

Sometimes all you need to save the world are words. At the end of Doctor Who Season 3, the Doctor was imprisoned by his childhood mate The Master.

Martha escaped but said that she would be back. During that time, she traveled the world telling people the story of The Doctor. Her long game culminated when she was recaptured by The Master exactly a year later, and the people she told the story to all thought the same word at the same time breaking a neural link.

That word was "Doctor."

Missy's plot to give The Doctor an army backfired on Doctor Who Season 8 Episode 12, "Death in Heaven."

Danny Pink, Clara's boyfriend who died in a car crash an episode earlier, didn't delete his emotions which left him outside of the hive mind of cybermen.

When the Doctor passed him a bracelet Missy intended as a cyber-controller, he was able to lead the army of Cybermen into the clouds where they burned. A bittersweet end to Danny Pink.

On Doctor Who Season 7 Episode 1, "The Asylum of the Daleks," the Doctor got some help from a woman named Oswin Oswald. Though she was able to help them navigate through the Asylum, a reveal that she'd been converted into a Dalek herself meant that he couldn't save her. But, Oswin had control over the asylum's systems she was able to clear a path to safety and save the Doctor and the Ponds.