There are many different versions of the tale of Chang'e (嫦娥). Here are three taken from Wikipedia which revolve around her and Houyi (后羿), a hunter.
Version 1
According to legend, Chang'e and her husband Houyi were immortals living in heaven. One day, the ten sons of the Jade Emperor transformed into ten suns, causing the earth to scorch. Having failed to order his sons to stop ruining the earth, the Jade Emperor (玉皇) summoned Houyi for help. Houyi, using his legendary archery skills, shot down nine of the sons, but spared one son to be the sun. The Jade Emperor was obviously not pleased with Houyi's solution to save the earth: nine of his sons were dead. As punishment, the Jade Emperor banished Houyi and Chang'e to live as mere mortals on earth.
Seeing that Chang'e felt extremely miserable over her loss of immortality, Houyi decided to journey on a long, perilous quest to find the Pill of Immortality so that the couple could be immortals again. At the end of his quest he met the Queen Mother of the West (西王母) who agreed to give him the pill, but warned him that each person would only need half the pill to become immortal.
Houyi brought the pill home and stored it in a case. He warned Chang'e not to open the case and then left home for a while. Chang'e became too curious: she opened up the case and found the pill just as Houyi was returning home. Nervous that Houyi would catch her discovering the contents of the case, she accidentally swallowed the entire pill. She started to float into the sky because of the overdose. Although Houyi wanted to shoot her in order to prevent her from floating further, he could not bear to aim the arrow at her. Chang'e kept on floating until she landed on the moon.
While she became lonely on the moon without her husband, she did have company. A jade rabbit (玉兔), who manufactured elixirs, also lived on the moon. The mythologies of Japan and Korea also feature references about rabbits living on the moon.
Another companion is the woodcutter Wu Gang (吴刚). The woodcutter offended the gods in his attempt to achieve immortality and was therefore banished to the moon. Wu Gang was allowed to leave the moon if he could cut down a tree that grew there. The problem was that each time he chopped on the tree, the tree would instantly grow back, effectively condemning him to live on the moon for eternity.
Version 2
Chang'e was a beautiful young girl working in the Jade Emperor's palace in heaven, where immortals, good people and fairies lived. One day, she accidentally broke a precious porcelain jar. Angered, the Jade Emperor banished her to live on earth, where ordinary people lived. She could return to Heaven, if she contributed a valuable service on earth.
Chang'e was transformed into a member of a rich farming family. When she was 18, a young hunter named Houyi from another village spotted her, now a beautiful young woman. They became friends.
One day, a strange phenomenon occurred - 10 suns arose in the sky instead of one, blazing the earth. Houyi, an expert archer, stepped forward to try to save the earth. He successfully shot down nine of the suns, becoming an instant hero. He eventually became king and married Chang'e.
But Houyi grew to become greedy and selfish. He sought immortality by ordering an elixir be created to prolong his life. The elixir in the form of a single pill was almost ready when Chang'e came upon it. She either accidentally or purposely swallowed the pill. This angered King Houyi, who went after his wife. Trying to flee, she jumped out the window of a chamber at the top of the palace and, instead of falling, she floated into the sky toward the moon. King Houyi tried unsuccessfully to shoot her down with arrows.
In contrast to the first version, her companion, a rabbit, does not create elixir of life. Aside from the rabbit, the moon is also inhabited by a woodcutter who tries to cut down the cassia tree, giver of life. But as fast as he cuts into the tree, it heals itself, and he never makes any progress. The Chinese use this image of the cassia tree to explain mortal life on earth — the limbs are constantly being cut away by death, but new buds continually appear.
Meanwhile, King Houyi ascended to the sun and built a palace. So Chang'e and Houyi came to represent the yin and yang, the moon and the sun.
Version 3
Chang'e was a human in the mortal world. She was a palace maid. Suddenly, 10 suns appeared in the sky and the earth became very hot. The king looked for a person with accurate archery skills to shoot down nine of the suns. A commoner called Houyi saw that the situation was getting bad. He took out his arrow and bow and shot down the nine suns with nine arrows. The King was pleased and wanted to reward him. Houyi was in love with Chang'e and wanted to marry her. The king gave her to him as a reward. The two lived happily until one day, a mysterious old man came and gave Houyi an elixir that could make him live forever. Houyi hesitated whether to take the pill. He was unsure and left the pill under his pillow on the bed. Chang'e found the pill. She did not know what it was and just swallowed it. Chang'e became immortal and flew to the moon. Houyi was devastated and died. People now use lanterns to light up the earth so that Chang'e can see them on the Earth.
Alternate versions
In one retelling of the story of Chang'e and the Elixir of Immortality, Chang'e's decision to consume the elixir is not caused
by selfishness or spite; instead, it is caused by fear of Houyi's apprentice, Feng Meng, who attempts to steal the elixir from
Chang'e. She consumes the elixir in order to escape him before the elixir can fall into Feng Meng's hands.