The doctor suffers from amnesia, but not complete amnesia.

"Dr. Kal'tsit, was the Doctor of the past really that terrifying?"
Watching one old fellow after another make new deals with the Doctor with expressions of fear and excitement, Amiya asked, somewhat puzzled.
"Yes... but that was a long time ago."
Kal'tsit won't tell Amiya the truth, but if you really want to know, you might as well turn the clock back twenty years.
At that time, the Witch King of Letania had just fallen from the tower, and all the Electors were eager to make their move—who had helped the twin queens secure their throne?
At that time, the former emperor of Ursus had been dead for four years, but the empire was still paying the price for his military gambles—who helped them get out of the shadows?
At that time, the conflict between the knights and merchants of Kazimierz reached its peak, and the two sides were just one step away from turning against each other with swords—who helped them suppress their burgeoning anger?
He forged alliances among the nations of Terra, exploiting their individual ambitions to seize the greatest benefits for himself—until the Tower of Babel pierced the throne of God.
"Actually, I really just wanted to save the world."
"—A sunny and warm-hearted PhD said with a smile."