Kono Yuusha, Moto Maou ni Tsuki

For a long time, the Demon King was hailed as the “strongest”. After defeating countless heroes who challenged him, he eventually grew tired of his life and drove a sword into his own heart. But when he came to, he had been reincarnated as a human baby in a world 1,000 years later...! Reborn as Zeon, the former Demon King enjoys a peaceful life as a human farmer. But by a twist of fate, he ends up being recognized as the hero of this generation?! The tale of a reincarnated Demon King dominating the world as a hero!! (Source: Square Enix, translated)