A mortal Knight, he is the champion of one of the Sidhe Courts. He gets powers in line with his court and he's the only one allowed to act in affairs that aren't directly related to the Sidhe. If the Queen wants an outsider dead, he is the trigger man, because a Queen cannot personally kill anyone not in her court.
In the seriesEdit
In Summer Knight, Mab tries to hire, rather forcefully, Harry Dresden to find the murderer of Ronald Reuel, an artist, and to return what was stolen from him. Bob informs Dresden that Reuel was the Summer Knight, and what was most likely stolen from him was the power of the position, the so-called "Mantle", that is bestowed upon the Knight.
Dresden discovers that the Summer Lady, Aurora, had the traitorous Winter Knight, Lloyd Slate kill the Summer Knight, Ronald Reuel so that she could unbalance the Courts. The Summer Lady was eventually defeated and killed,her plan thwarted and the mantle of the Summer Knight was released to find a new bearer, choosing Fix a young changeling, as the new knight of the summer court. The mantle of the Summer Lady was also released to choose its new bearer, choosing Lily, a young changeling as the new Summer Lady.