He was abusive, but though he seems to have adopted the teaching philosophy of "pain is an excellent motivator," he was more emotionally abusive and manipulative than he was so physically. He encouraged a distance between them and other children, and was gradually training the two of them to use violent magic without realizing that it was wrong, so that they would be his personal enforcers.
Justin DuMorne used to be a Warden of the White Council, apprenticed under Simon Pietrovich. He had participated in the hunt for the necromancer Heinrich Kemmler, on whose occasion he found and took the skull-bound air spirit Kemmler owned at the time, but kept its discovery and retrieval a secret from the White Council, who thought it had been destroyed. Some time later, he left the Wardens.
DuMorne adopted and apprenticed ten-year-old orphaned wizards, Harry Dresden and Elaine Mallory, shortly after they came into their powers. He began to teach them the basic principles of magic.(reference needed) One day, DuMorne turned Elaine into a thrall. He attempted the same thing on Dresden, but Dresden escaped. DuMorne sent He Who Walks Behind after him. Dresden came back to save Elaine Mallory. Dresden performed a fire spell, burning the house down, killing DuMorne.
He Who Walks BehindEdit
Harry Dresden had always assumed that DuMorne had sent He Who Walks Behind after him to be killed. Now Dresden considers the possibility that He Who Walks Behind hadn't really tried to kill him, but instead manipulated him into killing his mentor, and that He Who Walks Behind was quite possibly DuMorne's mentor, as opposed to DuMorne simply being the one who summoned and sent the Outsider after him.
In the seriesEdit
In Ghost Story, Harry Dresden recalls how DuMorne taught him his first fire spell: "Flickum bicus!", DuMorne gave him a Wilson baseball mitt. Later, Dresden recalls the day he came home early from school worried about Elaine Mallory and sensed black magic in the air. Elaine Mallory was sitting still, quiet, while Justin DuMorne stood at the kitchen doorway. There was a straightjacket on the table next to Dresden's copy of The Hobbit. DuMorne ordered Dresden to sit, and when he didn't, DuMorne sent a blast of kinetomancy at him who used the force to propel him through the window for an escape.