A lycanthrope is a person affected by a magical condition. They are first mentioned in Fool Moon.
Unlike the other various forms of werewolf, a lycanthrope is not a theriomorph. Physically human, they are indistinguishable from a regular person, at least on the surface. They are also unique in that they are born this way, and not made. A lycanthrope acts as a natural channel for a spirit of rage, which makes them beast-like, but only psychologically, so that they have "the minds and souls of beasts.". Driven by the spirit, they are more aggressive, stronger, and resistant to disease and injury; wounds heal very quickly, especially during a full moon, enabling them to survive much more physical damage than a typical human being.
In the series
In Fool Moon, a gang of lycanthropes known as the Streetwolves, are implicated, among others, in the Lobo killings. Harry Dresden is nudged to investigate them at the Full Moon Garage by Roger Harris of the FBI, and Dresden barely escape alive. Later the Streetwolves kidnap Dresden, but he narrowly escapes with the aid of Tera West and the Alphas.