The name quoted most often in the Talmud is Akiva. And he did not know his letters until he was forty.
The story begins at a well. He goes to draw water and sees a stone. The middle of it is hollowed out.
Water is soft and stone is hard. Yet the water carved the stone. Then how much could words, hard as iron, carve out my own heart. (Avot d’Rabbi Natan 6, translated directly)