When he was young, Di Yu was able to find the Key to open the
Prime Ominous Grave. He entered the Grave and managed to come back alive. He then hid for five generations of Immortal Emperors and ultimately, at a very old age, he shouldered the Heaven's Will and became an Immortal Emperor. People claimed that he had obtained something great from the Grave, something like an immortal scripture or a method for everlasting life, so that was why he could cultivate through five generations of Immortal Emperors and eventually become an Emperor himself. He did not live the longest after becoming an Emperor, but was definitely the oldest one. He managed to last through five generations of Immortal Emperors and became a miracle across the ages.