The earliest known descriptions of the Monkey King come from what is possibly the eldest book and certainly the longest in history. It is entitled "Journey to the West" and it describes the journey to the Monkey King to achieve enlightenment. It begins (according to what version you read) with the early days of the Monkey King. In some we see the Monkey King as being born from the immortal fires of the Earth and coming out of stone into being. He is described often as being half human, and half Monkey. He is often considered to have a tail and monkey like characteristics since he was raised by monkeys on the mountain of fruit and flowers. It was said that he had such amazing Chi power that it was like magic and at times as if he could fly from one mountain top to another moving like a simian.
Our earliest story involves Monkey King stealing his fighting staff, we are told it was two hundred pounds and that it was used by the Eastern Dragon to hold up the seas. It was not being used so Monkey King snuck down into the waters and into the palace of the Dragon King in order to steal it. Once he did Monkey King realized that he could shorten the length of the staff to the size of a pen and place it behind his ear. This staff has often been said to be the source of his incredible power but the point of the Monkey King is his child like behavior and spirit.
Other stories about the Monkey King involve the God learning the arts of shape-shifting as well as learning his 72 transformations. He could split into several different versions of himself or he could split into different beings entirely. He also learned to travel across the sky on a cloud and this of course was due to his pure heart and uncontrollable spirit which was like a child. That is one of the main points of the Monkey King, he uses the beauty soul to power the Chi magic he exerts. He has many other physical abilities, one of the most powerful is the power of super speed being able to run at some accounts of 250 miles per hour.
It has been said that one day as he sat on the throne in his mountain surrounded by his fellow Monkeys two men came down from heaven telling him that he would one day pass away. The Monkey King was upset and angered beyond average and so he charged up to heaven and broke into the dinner party being held by the heavenly Jade Emperor. It was here that the Monkey displayed one of his most distinguished traits, arrogance and instead of being upset the Jade Emperor was charmed and gave him the title of Monkey King. It was not until many years latter that he began to seek enlightenment under the Buddha and was imprisoned for a long amount of time by the Buddha. It is said that the Monkey King was clasped in the mighty hand of the Buddha and this became his prison for many years.
According to some it was now that the Monkey King had been given the chance to travel far away to the west with a monk searching for ancient scrolls and along this journey learned the ways of enlightenment. He studied under the monk and as they journeyed met up with several people much like in Dragon Ball when Goku met up with his friends on the way. After the journey Monkey King was given the name Sun Wukong and nearly every other story after this is said to be spun by people not the original text. The book itself has been published into four volumes and one hundred chapters. In this book the Monkey King begins to meet other figures from Chinese mythology as well as figures in history. This is a point in Chinese mythology which is not found in the west that is the art of bringing real people in history into the realm of myth.
Sun Wukong has been shown in nearly every form possible, he has been the star of popular manga comic books such as Dragon Ball, or the main idea in the movie Forbidden Kingdom. He has also been made into TV shows that have been adapted from the English language translation. He is one of the oldest characters in mythology and has had a large impact on real history. There have been two styles of martial arts that have been driven from this character and these are some of the higher forms of martial arts. One is Monkey style of fighting, where apparently one tries to imitate the movements of a monkey and the other is staff fighting. Both seem to be based on the concept of Chi energy that deals with your inner being and spirit.