Who is Monkey D Dragon's wife/Luffy's mother? In around chapter 592-596 of One Piece, Buggy the Clown mentioned that Silver Rayleigh is Luffy's uncle. This implies that Rayleigh's sister should be Dragon's wife.

Who is Monkey D Dragon's wife/Luffy's mother?
No mention has yet been made of Luffy's mother at all, the idea of her hasn't even been brought up. Very few characters have been mentioned to have mothers at all for some reason.

In Japanese as in many Asian countries, they use the idea of "Uncle" or "Big brother" differently to in English speaking countries. It just means an older person you respect, and doesn't imply a blood relation at all. By far most likely what happened is Buggy called Rayleigh "Uncle Rayleigh" as Rayleigh used to be his first mate when he was a cabin boy.

So in summary, there is nothing said about Luffy's mother, nor any hints given, and it's incredibly unlikely that Buggy was saying that Rayleigh is Luffy's uncle, which doesn't happen in the manga anyway.