Leanan sidhe is a vampiric fairy that pertains to Irish folklore and is most of the times depicted as a muse for artists.
While inspiring them to create remarkable work, the leanan sidhe feeds off their life-force. She is described as a beautiful mystical creature that takes human lovers.
The most commonly used description of the leanan sidhe is that of W. B. Yeats:
The Leanhaun Shee (fairy mistress) seeks the love of mortals. If they refuse, she must be their slave; if they consent, they are hers, and can only escape by finding another to take their place. The fairy lives on their life, and they waste away. Death is no escape from her. She is the Gaelic muse, for she gives inspiration to those she persecutes. The Gaelic poets die young, for she is restless, and will not let them remain long on earth—this malignant phantom.
She is used more and more in modern literature and tv series.