The Advocate
The Advocate was an alien who had escaped the Time War after Dalek Caan saved Davros, following him through into the normal universe as the Last Great Time War was Time-locked. (IDW: Don't Step on the Grass)
The Advocate first met the Doctor when she was at the Shadow Proclamation. She represtented him as his solicitor after they put him on trail for saving Emily Winter's life. The Advocate then found out that "Finch" on the Prosecution had set the Doctor up. She tried to sort it out, but was shot by a Judoon, after "Finch" told her to shut up, apparently killing her. However, this sent her back in time to the final events of the Time War; she was left insane and dangerously intelligent. After suffering countless deaths and lives, she found Dalek Caan and used his path as an exit route from the War. Already blaming the Doctor for what happened to her, the Advocate observed his actions over the millenia it took her to reform herself and deemed him a threat and began to hate him deeply. Some time later the Advocate found the Gizou who would impersonate Finch and hired him so that he would send her past self to the Time War. (IDW: Don't Step on the Grass)
She then reappeared in the Finch imposter's cell after he had been found out as a Gizou. He said he was sorry that he failed her, but she said the Doctor held the final part of a puzzle and with the Shadow Proclamation believing her dead that she can move through time and space undetected. (IDW: Fugitive)
Soon after, she staged an attack on the TARDIS by a group of insectoid aliens, damaging the dimensions within, so that she could steal an artifact. While within the unstable TARDIS, she encountered Matthew Finnegan and tried to convince him that the Doctor preferred Emily over him and that he could not be trusted. She left him a false copy of the diary of Vislor Turlough to implant even more doubts of the Doctor's good nature in Matthew's mind. (IDW: Tesseract)
Later she set up the Doctor so that he would locate the Enochai beneath Greenwich Park in 2009. She manipulated Crane into releasing the majority of them, and presented herself as a possible saviour to Erisa Magambo, with Matthew vouching for her trustworthiness. She propesed destroying the Enochai' ship beneath the park using a bomb, which would have cost many lives. When the Doctor managed to arrive back to the UNIT camp, he was arrested when he protested against the Advocate's plan. Once freed, he reached Crane, who was trying to redeem himself by placing the bomb, and flew the ship away from Earth so that the Enochai would be pulled with it. However, the bomb was armed and Crane could not leave it without setting it off. The Doctor and Crane realised this had been the Advocate's intention all along: punishing Crance for his betrayal and teaching the Doctor a lesson. The Doctor escaped and Crane let the ship and himself explode. The Advocate blamed the Doctor and prepared to depart, this time joined by Matthew. (IDW: Don't Step on the Grass)