Thirteenth Doctor

The Thirteenth Doctor was the first female incarnation of the Doctor.

Biography
The Twelfth Doctor had been gravely wounded by the Cybermen on the Mondasian colony ship. In spite of his life-threatening injury, the Doctor, feeling tired of "being someone else", chose to purposefully halt his regenerative process. (TV: The Doctor Falls) However, following an encounter with his first incarnation, who had held similar reservations before his own regeneration, and the Testimony, the Doctor ultimately conceded that another regeneration would not "kill [him]."

Returning to the TARDIS, the Doctor addressed himself or rather his successor, offering words of advice before finally regenerating. Immediately after, the Doctor examined her new face in a reflection, to which she simply exclaimed "Brilliant!" However, before she could continue, the TARDIS suddenly fell out of her control, and the Doctor found herself falling out through the TARDIS' now opened doors to the Earth below. (TV: Twice Upon a Time)