The Seven

The Seven was the main alias used by the seventh incarnation of a Renegade Time Lord who suffered from regenerative dissonance.

The Seven was known for being rude and abrasive. Indeed, the Nine thought that him congratulating the Eleven was rare. He was also the more scientifically inclined incarnation. He was used by the Eleven to portray a scientific advisor. (AUDIO: World of Damnation, Sweet Salvation)

When the Nine was aiming for kidnapping all of the Doctor's companions, River Song told him to retrieve Katarina's dead body, as that would be the only way to get a "complete collection". In fact, her body was being guarded by a younger version of River, who confronted the Time Lord, giving the older River a chance at escaping. It was the Seven who realised her plan and warned his future self to go back to the TARDIS. (AUDIO: Companion Piece)