Snow White/Mary Margaret Blanchard
As a young child, she unintentionally tells Regina's mother a secret involving Regina's secret relationship with the stable boy, causing Cora to kill him and Regina to become the Evil Queen. Since then, she had been on the run from her, eventually meeting Prince David, who she nicknames as Charming. She is later placed under a sleeping curse by the Evil Queen but broken by Charming. The two get married, but is threaten by the Evil Queen with a curse. In order to defeat her, Snow and Charming send their daughter Emma to the Land Without Magic.
In Storybrooke, she appears as Mary Margaret Blanchard, a teacher at Storybrooke Elementary School. After the curse broke, she is reunited with Charming, now known as David, as well as her daughter Emma and grandson Henry. She is responsible for the death Regina's mother. Later, she follows the rest of the heroes to Neverland to save Henry and is eventually sent back to the Enchanted Forest after Regina undid her curse. She later cast the curse to bring everyone back to Storybrooke to protect her unborn child from the Wicked Witch of the West. She also clashes with Maleficent after Maleficent threatens to reveal a dark secret of her past. After Emma becomes the Dark One, she goes to Camelot with the heroes to help save her and later to the Underworld with Emma to save Hook. She also accidentally gets send to the Land of Untold Stories with David, Hook and Zelena, but is eventually brought back to Storybrooke.
Credit: Wikipedia