The Jade Emperor in Chinese Mythology, and an important deity in Taoism. You might also know him as Yü-huang, Yu-di, or Shang-di. He is the head honcho of the Chinese deities, although there are others competing for this honour.
Yu-huang was originally the assistant of Yuan-shi tian-zong (the 'Celestial Venerable of the Primordial Beginning'). Yuan-shi tian-zong is still around, but has given charge of all worldly and heavenly administration over to Yu-huang. With the event of Buddhism, some stories of Yu-huang tell how even he has accepted Buddha as a higher authority, although I doubt that the Taoists would agree. Yu-huang has also had some competition form the Monkey King, a supervillian of great powers.
Yu-huang was originally the son of the mortal emperor Ch'ing-te and his wife, Pao Yueh-kuang. When his father died he accepted the throne, but abdicated after only a few years (or days, depending which version you believe). Free of the duties of ruling, he took up the study of the Taoist texts; after much study, he finally achieved perfection, and traveled about teaching what he had learned to others. After an extraordinary amount of time, he finally became one of the 'golden immortals', and aeons later Yuan-shi tian-zong decided he was fit to rule.
Yu-huang is in charge of all that happens in heaven and earth, mostly by proxy. Once a year all the gods report to him, and he gives them their instructions. He spends most of his time dispensing justice, in the form of punishment for bad deeds and thoughts. He lives in a palace in Da-luo-tian, the highest of the Taoit heavens.
Despite most of this writeup referring to Yu-huang as a Taoist deity, he has become an important Buddhist figure.