Tasha Lem

 was the Mother Superious of the Papal Mainframe, and an old friend of the Doctor. Shortly before the Siege of Trenzalore, she summoned the Eleventh Doctor and Clara Oswald aboard the Papal Mainframe. After explaining how to breach the force field she erected around Trenzalore, she sent the Doctor and Clara to the planet's surface, ordering them to return to her in "one hour".

When the Doctor later discovered that Gallifrey and the Time Lords were attempting return through the scar tissue left by the Cracks in Time, Tasha contacted the Doctor via a massive holographic projection of her face and warned him not to summon the Time Lords back, or else the Time War would begin anew. The Doctor refused to abandon Trenzalore's people. In response, Tasha informed the Church that their new faith would be "Silence". She declared that the Doctor must never speak his name and that "silence will fall."

Three hundred years later, the Daleks - having failed to breach Trenzalore's defenses on their own - attacked the Papal Mainframe and killed everyone inside, including Tasha. The knowledge of the Doctor was extracted from her corpse and used to restore the Daleks' lost memories of him. The Daleks also apparently revived, tortured, and killed her several times in a failed attempt to learn how to fully breach Trenzalore's defenses. Eventually, she was converted into a Dalek puppet. The Daleks used her to draw the Doctor and Clara into a trap onboard the Papal Mainframe, under the guise of wanting to speak with him.

During the feigned conference, she explained to the Doctor how Madame Kovarian and a renegade faction of the Church of Silence were responsible for the attempts on his life. Upon revealing that she was actually killed in the Dalek attack three days prior, her Dalek conditioning activated and she transforms into a Dalek Puppet, just as three Daleks entered the room. The Doctor threatened to speak his name, bringing back the Time Lords - and with them the Time War itself. In response, Tasha took Clara hostage, and the Daleks threatened to have Clara killed if the Doctor didn't "die in silence".

The Doctor told the Tasha-Dalek to kill Clara, claiming he didn't care. Clara did not see this as a betrayal, however, as she understood the Daleks planned on killing her anyway, and instead remained by the Doctor's side. The Doctor praised Clara's bravery and berated Tasha for her cowardice. These insults brought Tasha's personality back and (after slapping the Doctor) she proceeded to destroy the three Daleks with her Dalek-implanted weaponry. She then told the Doctor and Clara to flee, warning them that she couldn't resist the Dalek programming forever. The Doctor - refusing to abandon the people of Christmas - urged her to continue fighting the Dalek conditioning. She took his advice, and after the Doctor and Clara escaped back to Christmas, Tasha proceeded to rally the remaining Church and Silent forces on Trenzalore to fight alongside the Doctor.

When the Doctor was dying of old age, Tasha piloted the TARDIS to retrieve Clara so that she could be with him. (TV: The Time of the Doctor)