Joan of Arc is the only Catholic saint who was originally declared a heretic and burned at the stake by the Catholic church.
She was certainly a remarkable person by any criteria. She was a village girl, born in Domrémy in Lorraine (France) around 1412. By this time, the fifteenth century, people had last names; hers was d'Arc (so she has nothing to do with Noah's Ark, some student exams to the contrary). From girlhood, she had visions of saints who spoke to her.
There is no question that she heard voices. In the Middle Ages, the question was whether these were the voices of saints or angels. Angels were decided on definitively in the early twentieth century, when she was declared a saint, but for many historians the question has been which psychological condition she suffered from. Different eras seek different explanations.
At the age of 17, under the inspiration of the angelic voices (as she certainly considered them), she set off to meet with Charles VII. He was living in exile, not yet crowned, because the Hundred Years War was going on, and the English held northern France, including Reims, where French kings were traditionally crowned. She managed to persuade him that the saints wanted him crowned, and he provided her with armor and knights and sent her off to Orléans, which was held by the English.
Here, to everyone's surprise except perhaps her own, she inspired a great victory. (You can still buy Jeanne d'Arc refrigerator magnets in the gift shop of Orléans cathedral.) With this victory, it was now possible for Charles to cross the Loire into northern France, and Joan got him to Reims and got him crowned.
She continued to have success against the English, enough that Charles may have become jealous of her reputation. When she was captured in battle, he made no attempt to ransom her. The English tried her for heresy, based in part on the voices and in part on a charge of cross-dressing, found her guilty (no surprise), and had her burned at the stake in 1431. She was still only nineteen. (How many of us have led victorious armies in our teens, defying all gender expectations? It would be good to skip the part about being burned at the stake, however.)
The French never believed she had been a heretic, and in the following years, inspired in part by her example, they finally drove the English out of France and ended the war. The pope was persuaded to reopen the case in the 1450s and declared that it had not been a fair trial, although she was not officially made a saint until 1920.