That was Denton, inside. A good man, jaded by years and poisoned by the power that had taken control of him, until that good man had been buried and only the filth and decay remained. Until the existence of the man who had once been was only a bitter reminder that made the man who was now seem all the more downfallen by comparison.— Dresden, on his Soulgaze with Denton
Phillip Denton was a FBI agent that Karrin Murphy had called in on the Lobo killings case for access to FBI resources. He and his team Agent Benn, Agent Harris, and Agent Wilson took over the case. Later, it comes out that he and his agents are Hexenwolves—a form of lupine theriomorph, who transformed into a wolf by use of a belt.
Agent Denton was 6'3" or 6'4". He had black hair and pale grey eyes. He appeared to be over 40 years old.
Denton made a deal with some unknown source, possibly the Black Council, for the wolf belts. Originally the plan was to use the belts to take down Gentleman Marcone as wolves to circumvent the law. In order to throw off any magical investigation, they attempted to set up both the Streetwolves, a gang of Lycanthropes, and Harley MacFinn, a loup-garou.
As the wolf belts were black magic. Denton and his agents began to abuse the power of the belts. Eventually they became, in Harry Dresden's terms, addicted. Their blood lust ran out of control and innocents were killed. Denton dismissed these murders as necessary sacrifices.
In the series
In Fool Moon, Harry Dresden was called in by Karrin Murphy to help the Special Investigations team investigate the Lobo killings. He eventually works out that Denton and his agents are behind them.
There is a showdown at John Marcone's estate. After a fight where his three agents were killed, Denton took on Dresden, who had used one of the wolf belts, and lost. He survived when Susan kept Dresden from killing and falling under the influence of the belts, just as Denton had.
In Proven Guilty, it is implied that the Black Council is behind the wolf belts that made Denton and his agents turn Hexenwulfen, as well as: Shadowman, the Nightmare, the Summer Lady Aurora and the Red Court all being more powerful and more connected than they should be. Plus: the Fetch taking Molly to Arctis Tor and Hellfire used there, and a highly placed traitor on the White Council.
In Cold Days, the Summer Lady, Lily, implied that the Contagion—later named Nemesis—corrupted Dresden's first three big cases: Victor Sells the Shadowman, Agent Denton and his hexenwolves, and Leonid Kravos.