The Union was an incarnation of a Renegade Time Lord who suffered from regenerative dissonance.
She created the Diamond Array as a way to control the dissonance in her mind. She used the calm of her meditation room coupled with the Degeneration energy from captured Time Lords to control this. She collected degeneration energy from the Doctor, the Master and the Corsair and planed to take similar energy from the Monk. She captured The Two to help pilot her ship and control the engines she used to convert star systems into Diamonds for her collection. When the Doctor returned to the Diamond Array he undid her plans with the help of River Song and Susan Foreman, and her regenerative dissonance returned. (AUDIO: The Union)