The Inquisitor was part of the Baspral justice system.
Ten years later, the Inquisitor saw the boy, grown to a man, drown Galena in the very stream in which she tried to drown him. The man became a dictator and started the Great Cleansing, in which the Inquisitor, as a member of the militia, took part.
Several years later, after Baspral had recovered from the Great Cleansing, the Inquisitor captured the Sixth Doctor for execution. In the Doctor's cell, he questioned the Doctor. Little by little, he was brought round by the Doctor to admit that he himself wanted to be executed instead for participating in the Great Cleansing. He freed the Doctor, intending to die in his place.
However, the Doctor rescued the Inquisitor from execution. To maintain the fiction that the Inquisitor had been executed, and thereby start the impetus for a change in Basprali laws, the Doctor removed the Inquisitor from his time and took him to the Time Vortex with others who had been removed from their times. (PROSE: The Inquisitor's Story)