Who was Karwa Mata & how did she inspire tradition of Karwa Chauth?

Karwa Mata was a devoted wife who saved her husband from a crocodile by seizing it with cotton yarn and asked Yama, the God of Death, to send the crocodile to hell, or else she'd curse him. Yama blessed her husband with a long life. This inspired the tradition of Karwa Chauth, when wives observe a fast for their husbands.