Time Lord Victorious

The death of Amy
The beginning of the Doctor's downward spiral began after an encounter with a group of Dalek drones ended with not only the destruction of the Dalek fleet and their mothership but the death of Amy after a stray blast from a Dalek weapon hit her. The Doctor never forgave himself after she died and apparently Rory never forgave him either.

Rory's suicide and the Doctor's breakdown
Rory blamed the Doctor for Amy's death and kept his inner pain and angst suppressed until he could take it no more and ejected himself from the TARDIS while it was in space, sucking himself into the vacuum. Before killing himself, Rory venomously proclaimed that Amy died because of the Doctor and that everyone he encounters is corrupted or destroyed by association.

This proclamation, added with the deaths of both Amy and Rory in so little time broke the Doctor's spirit. Realising that he indeed has caused such harm to the universe with his methods and rules, he decides that helping the Universe is a trivial pursuit. Instead, he will do the best he feels he ever will be able to do for the universe - control it.

The Second Fall of Gallifrey
The Doctor, filled with rage and pain, decided that the universe needs order but not from the corruption and eventual megalomania of the Time Lords or any other higher civilization. He used his TARDIS to send several different armies from countless worlds to lay a full-frontal assault on New Gallifrey. In mere hours, he once again brought the extinction of his race and his homeworld was reduced to a volcanic wasteland. With the armies' purpose now fulfilled, the Doctor tricked them into entering a supermassive black hole and destroying them.

The Galactic Coup
The Doctor then began decimating all governments and political powers across the universe, outwitting all of them and ruthlessly slaughtering all in his path. The Shadow Proclamation fell, and soon all others followed. The Doctor then proclaimed to the entire universe that he has taken power over the governements of the entire universe and all who oppose him shall be wiped out. Staying true to his word, all protests and rebellions were dealt with swiftly.

To demonstrate his power and how clear he wanted to be in showing just how much he is willing to push to assert it, he vapourised Earth without batting an eyelid and had all the other civilizations watch and see him destroy his most beloved planet and showing absolutely no remorse. His title of 'Doctor' was then abandoned and replaced with 'the Time Lord Victorious' - Lord of Time, Controller of All Life in the Universe.

The Great Purge
The Time Lord Victorious began shaping things to bend to his will. He began destroying the planets of every creature who dared defy him in the past. This included Sontar, Raxacorricofallapatorious and even Ood-Sphere - trillions of lifeforms snuffed out by the Victorious and his army of robotic soldiers. The Victorious wanted to make sure that all major threats were dealt with so that no one would dare defy or challenge his word.

The Daleks tried to wage war on the Victorious but the entire remnants of their armies, colonies and eventually their species were destroyed. The Victorious had indeed reigned supreme and his rule was unmatched and unchallenged.

Appearance
As the Victorious, the Doctor abandoned his previous attire. He instead wore a black shirt and trousers and a large black coat. For some reason, his skin became much paler and his eye sockets darkened and his eye colour changed into this dark amber-red. His hair is much more messed up and unkempt.

Abilities
The Victorious has all of the Doctor's intellect, equipment and his own TARDIS. What makes him differ is his arsenal of weapons and no qualms in using his combat skills.

Personality
His personality is a very sadistic, remorseless and arrogant nature. He has no empathy for anything, killing trillions of people and causing mass panic and mayhem, sometimes for something as small as making a point to someone or more frightening of all, for no reason other than he wanted to. His despair over the deaths of Amy and Rory and the realization that he has caused fear and death unwittingly is what sparks him to simply give up and do it willingly, caring for nothing other than his rule, which he may believe is him doing the right thing by making him the greatest and only threat to life in the universe, or he simply just went insane and power-mad. The Victorious is a monster in its purest form: unrelenting, unsympathetic, remorseless, practically immortal and nigh-unstoppable.

Trivia

 * The design and concept of the Victorious was to be 'a blend of the Doctor, Palpatine, the Plutonian from Iredeemable and the Master'.
 * The creation of Amy and Rory androids is similar to Penthos' creation of cyborg 'children' in The Death of Hope.
 * The Victorious' death toll is referenced in the episode to be 'nearly 400 thousand trillion'.