when was it established that time lords can change gender
Regeneration (Doctor Who) Whether Time Lords could change gender in regeneration was never addressed onscreen during the classic series and not explicitly focused on for much of the revival. In the second part of The End of Time (2010), the Eleventh Doctor briefly checks for an Adam's apple upon regeneration to confirm if he is still a man. In "The Doctor's Wife" (2011), he reminisces about an old friend and fellow Time Lord, the Corsair, who had been both a man and a woman several times. In "The Night of the Doctor" (2013), the Sisterhood of Karn specify the Doctor could choose to change sex using one of their elixirs which influence the outcome of regeneration. "Dark Water/Death in Heaven" (2014) shows that the Doctor's longtime nemesis the Master has become a woman, taking the name Missy. In "Hell Bent" (2015), the Time Lord General regenerates into a younger woman, and states that her previous incarnation was her only male form. In "World Enough and Time" (2017), the Doctor tells his companion Bill Potts, in reference to Missy, that Time Lords are mostly beyond gender norms and stereotypes; however, Bill points out that the males and females of the species collectively refer to themselves by a male title. From "Twice Upon a Time" onward, Jodie Whittaker will portray the Thirteenth Doctor, the Doctor's first female incarnation.