The Valeyard

The Valeyard was the prosecutor during the trial of the Doctor. He presented past events in the Doctor's life as extracts from the Matrix and used them as evidence of the Doctor violating the non-interference policy of the Time Lords. He later charged the Doctor with the crime of genocide against the Vervoids.

The Valeyard had secretly tampered with the Matrix extracts to show the Doctor in the worst possible light and steer the trial to a guilty verdict. The Master revealed that the Valeyard was actually the Doctor himself "between his twelth and final regenerations'' or perhaps the essence of the Doctor's dark side from that time.


 * The Master's statements seem ambiguous on this point, leaving many mysteries open concerning this statement.

Acting on behalf of the High Council to cover up the Ravolox affair. As payment, the Valeyard would receive the Doctor's remaining regenerations. (DW: Trial of a Time Lord)

Other timelines
In one timeline, the Valeyard did manage to defeat the Doctor and went on to wreak havoc throughout time and space. (DWU: He Jests at Scars...)

Behind the Scenes
The Emissary of Death was a story scripted for the unmade season 27 of the original run of Doctor Who. This story would have featured the return of the Valeyard, where he attempted to not only frame the Doctor for committing the Jack the Ripper murders, but also for breaking the laws of time by committing them two years early. The plot element of the Valeyard being Jack the Ripper would be reused in Matrix.