Curly Dadan is a friend of Monkey D. Garp’s and the foster mother of Portgas D. Ace and Luffy. Garp entrusted her to take care of Portgas D. Ace shortly after the boy’s birth. Later, Garp also left Luffy in Dadan’s care.

Dadan lives on Mt. Corvo near the Windmill Village. She is the Mt. Corvo mountain bandit boss of the Dadan family and a wanted criminal.

She was first mentioned after the Enies Lobby incident when Garp come to Water 7, which he claims that he left Luffy and Ace to train with a friend. Her name was first mentioned by mayor Woop Slap after he saw Luffy new bounty and questioned “Does Dadan know!?”.

(Source: One Piece Wiki)