rose tyler, defender of the earth: the day of the doctor
"I hear you. All of you. Jangling around in that dusty old head of yours. I chose this face and form especially for you. It’s from your past. Possibly your future, I always get those two mixed up. I think I’m called.. Rose Tyler. No. Yes. No, sorry. In this form, I’m called Bad Wolf. Are you afraid of the big bad wolf, Doctor?”
Rose Tyler created the Bad Wolf. Bad Wolf then sent her sentience and conscience into the Moment. At the end of Season One, we saw the Bad Wolf end the Time War—not by killing all the Daleks _and_ everyone else, but by simply killing the Daleks. In fact, the first Daleks she killed—in the episode Dalek and in the Parting of the Ways—were both killed with their own weapons. Remember? But she caused it. She does not help the Doctor fight or end the Time War. She does it for him, so he doesn’t have that guilt. Bad Wolf is a weapon in one moment of time. And in the Day of the Doctor, we see that as the weapon known as the moment, who can commit multiple cases of genocide in just a moment, she again prevents the Doctor(s) from having to carry that guilt. She causes the Time War to end and kills all the Daleks (that were currently involved in the War, anyway) by using their own weapons against them. Maybe the Day of the Doctor didn’t have Rose Tyler as we normally know her, but it did have her in the aspect of her that was always most vital to the Doctor—as the one who saves the Doctor from himself.