Here's my theory on Cora, Regina's mother....

She's the miller's daughter that Rumple encountered in the original fairy tale. In this version she and her drunken single father are dirt poor and in debt and and very early on in her childhood she resloved to escape her life as a peasant. Since her father is constantly drinking Cora runs the mill and takes care of the house all by herself with no help from anyone. She meets Rumple in the town square one day and he tells her that she is destined for greatness and power. Cora is intrigued but she doesn't believe him at first. But then one day her father makes a drunken boast that his daughter can spin straw into gold and this gets back to the greedy King whose son, the Prince, is Cora's future husband. So Cora is brought to the palace and is forced to spin three rooms full of straw into gold. One room every night by the impending dawn or she will rot in the dungen forever otherwise if she succeeds she will marry the Prince. Rumple re-appears every night to help her but on the third she has nothing left to give him so he says that when she marries the Prince that her first born child will belong to him. Cora agrees and eventually marries the Prince who she doesn't love she just sees him as a ticket out of poverty. Then two years later Regina is born and Rumple comes to claim her. Cora makes another deal with him, if she can guess his name by sunset in three days time he will let her keep her daughter but if not Regina is his to keep. Cora succeeds in guessing his name and keeps Regina but Rumple actually gives her half of his powers and offers himself to her as a mentor to help her use her powers in exchange for immunity.

When Regina becomes evil after Daniel's death, Cora helps her daughter with her powers but then Regina finds out about her mother's past deals with Rumple who has become an enemy of the kingdom but he can't be arrested. Regina confronts her mother and they have a heated disscussion which becomes a talk about Daniel. Regina then kills her mother and gets her powers making her more powerful than her mother but not Rumple.