Defrabax was known as a mage. He could not call himself a scientist, since scientific investigation was illegal where he lived. He wanted to destroy the Furnace and activate a reactor that would provide everyone with power, not just the rich. His plans went awry when the Mecrim attacked, and the reactor was blown up so the Mecrim could be defeated. The explosion also killed his apprentice Cosmae.
Feeling responsible for his death, Defrabax chose to atone by entering into negotiations with the Rocarbies and Dugraq so they could live on the surface with the humans in peace. (PROSE: The Menagerie)