The Canterbury Tales: The Wife of Bath's Tale
The Loathly Lady
This lady gives a roughly 120 line speech on the origins of 'gentilesse' and the virtues of poverty and ugliness as a rebuke to the knight's castigation of her for being ugly, old, and low-born. The speech seems to have had a real effect on the knight, because after it, he proves himself reformed of his bad attitude. Before the speech, the loathly lady tells the knight the answer to his burning question, and her answer saves his life. Then, she forces him to marry her, which teaches the knight either to keep his promises, or not to make promises he doesn't know he can keep. The knight learns a lot from her – heck, he's alive because of her – so she's definitely a mentor to him as he navigates his way through his adventures.