The Leanansidhe

The Leanansidhe is a faerie of the Winter Court. In Celtic myth, the leanan sídhe ("fairy mistress") is a fae known for taking human lovers and providing them with artistic inspiration, at the cost of madness and an early grave.

Biography
Leanansidhe has lots of curly copper and scarlet hair, and amber eyes.

She made a deal with Harry prior to his duel with Justin DuMorne and during the course of Grave Peril.

Leanansidhe is Harry Dresden's faerie godmother. He was in her debt before she sold his debt to Queen Mab.

Harry mentions on several occasions that Lea and his mother were close. This is demonstrated by some of Lea's actions in which she credits Maggie in Harry's stead.

Leanansidhe is considered one of the higher sidhe within the Winter Court and held a position of power up until her imprisonment by Mab. Subsequently, in Changes, Mab refers to the Leanansidhe as her handmaiden and notes that she is second in power within the Winter Court only to Mab herself.

In Proven Guilty Leanansidhe is shown to be trapped in Arctis Tor, during which she exhibits signs of a personality more ruthless and devious than her dominant one.

The Leanansidhe claims in Changes that she was being treated for an ailment by Mab during her imprisonment. Despite such 'treatment,' it is still readily apparent that, by mortal standards, the Leanansidhe is less than mentally sound, evidenced by her childlike behavior and excitement at times of extreme violence such as Harry's victory in the duel near the conclusion of the book.