The Valeyard appears in all four segments of Trial of a Time Lord - The Mysterious Planet, Mindwarp, Terror of the Vervoids and The Ultimate Foe. In episode 4 of The Mysterious Planet it is stated that valeyard means learned court prosecutor .During the course of the trial, the Doctor was accused of conduct unbecoming a Time Lord and transgressing the First Law of Time. As prosecutor, the Valeyard presented the events of The Mysterious Planet and Mindwarp as extracts from the Matrix, the computer network that serves as the repository of all Time Lord knowledge. The Valeyard used these extracts as evidence of the Doctor's meddling in time and space. Throughout the presentation of the evidence the Doctor barracked at the Valeyard, calling him names such as the Boneyard, the Scrapyard, and the Knacker's Yard, and only the interventions of the Inquisitor, another Time Lord, kept the trial going.What was not discovered until later was that the Matrix extracts had been tampered with to show the Doctor in the worst possible light. In The Mysterious Planet this involved the editing of particular scenes. Scenes of the mercenary Sabalom Glitz attempting to buy secrets from the robot Drathro were censored completely. In Mindwarp substantial portions of the extract were falsified entirely by the Valeyard. The most significant alteration was when the Time Lords intervened in the brain transplant experiments of Lord Kiv and his scientist Crozier. In the Matrix extract, it appeared that Yrcanos was possessed and that he killed the Mentors and the Doctor's companion Peri.When the Doctor presented in his defence the future events of Terror of the Vervoids, he began to suspect that the Valeyard was tampering with the evidence, but lacked proof. The Doctor was forced to destroy the human-plant hybrids known as the Vervoids when they ran rampant on a space liner. If they had been allowed to reach Earth they would have eliminated all animal life. The Valeyard tampered with the scenes and made it appear as if the Doctor had committed genocide.In The Ultimate Foe, the Master appeared in the Matrix, revealing that it was possible to infiltrate it. Sabalom Glitz and the Doctor's future companion Melanie Bush were presented to the Court to rebut the Valeyard's accusations. It was then revealed that the Valeyard was, in fact, the Doctor himself or rather, a distillation of the Doctor's evil side, a potential dark version who might exist between his twelfth and final incarnations. This concept is similar to the ethereal Watcher that manifested itself to bridge the gap between his fourth and fifth incarnations (Logopolis). However in the novelization of the story the Master states The Valeyard, Doctor, is your penultimate reincarnation ... Somewhere between your twelfth and thirteenth regeneration implying that the Valeyard is the thirteenth incarnation of the Doctor. ( Twin Dilemma revealed that Time Lords do have a thirteenth regeneration but because there normally is not a fourteenth incarnation using this last regeneration is generally fatal for a Time Lord.)The Valeyard was also revealed to be acting at the behest of the High Council of Time Lords to cover its corruption in the Ravalox affair. The secrets were information from the Matrix. Ravolox was Earth, but the Time Lords moved it through space, killing virtually every human being living on it. To prevent the Doctor discovering the secret and revealing it, they used the Valeyard to try to have the Doctor executed under the pretence of a trial. The reward for the Valeyard's actions would have been to give him all of the Doctor's remaining regenerations and make his existence concrete. However, the Valeyard would then have slain every member of the Court as well, using a particle disseminator located within the Matrix.The Doctor entered the Matrix and fought and defeated the Valeyard in a fictional world of his creation. The Inquisitor revealed that Peri had indeed survived and was married to Yrcanos. The Master and the Valeyard appeared to be trapped in the Matrix, but at the end of the serial, the Valeyard was seen disguised as the Keeper of the Matrix. The subsequent whereabouts of the Valeyard have never been disclosed in the television series. It remains to be seen if the Valeyard will still manifest himself when and if the Doctor, now in his tenth persona, reaches his final regeneration.In one timeline, the Valeyard did manage to defeat the Doctor and went on to wreak havoc throughout time and space. (Doctor Who Unbound: He Jests at Scars...) Show less «