Unlike the current top answer, the Lilith predates the christian belief system. Lilith was according to the Alphabet of Ben Sira, was the first wife of Adam. In no other ancient text does it state that. In the Alphabet of Ben Sira, Lilith refused to be submissive to Adam, and Adam refused to be equals. Lilith then left, and God created a new wife for Adam. Lilith shows up well before that text in ancient hebrew texts. Those refer to her as a demon who represented lust much like the demon Asmodeus in other texts. Lilith was historically shown as a purely evil figure up until the creation of the Alphabet of Ben Sira, which is considered to be a satirical work by most scholars.
Lilith is a figure in Hebrew Mythology.