Thread:LucidPigeons/@comment-25008763-20150319022307/@comment-25008763-20150319040424

basically the Valeyard wanted to steal the Doctor's remaining regenerations and keep them for himself, ridding himself of his "other half" : to do this he manipulated the other Time Lords into hosting a trial, with the intention of murdering all present after they'd served his purpose.

He manipulated the Matrix to show the Doctor in a very negative light in order to try and secure a definite "guilty" (and thus get his regenerations) : ironically Doctor was only saved when the Master revealed Valeyard's trickery (having enjoyed seeing Doctor suffer but not wishing to see him die (at least by Valeyard) ).

He escaped capture and was pursued by Doctor, who stopped him using a particle weapon to destroy the Court (once again trying to kill everyone present) : Valeyard was apparently destroyed after that (but like many Who villains it is later shown he survived). <- this was all his first appearance, after this he went on to do many horrible things..

By far his most EVIL act was becoming Jack the Ripper, using a Dark Matrix to corrupt past Doctors into committing crimes on his behalf and feeding the machine using victims, uncaring of the ravages it caused time.. his appearances are far too vast to list here :

http://tardis.wikia.com/wiki/The_Valeyard  (a brief skim of this article can provide some details on his many crimes (it is also reliable as it is all about canon Who lore) )