In the Tibetan Buddhist pantheon of enlightened beings, Chenrezig is renowned as the embodiment of the compassion of all the Buddhas, the Bodhisattva of Compassion.
Avalokiteshvara is the earthly manifestation of the self born, eternal Buddha, Amitabha. He guards this world in the interval between the historical Sakyamuni Buddha, and the next Buddha of the Future Maitreya.
According to legend, Chenrezig made a a vow that he would not rest until he had liberated all the beings in all the realms of suffering. After working diligently at this task for a very long time, he looked out and realized the immense number of miserable beings yet to be saved. Seeing this, he became despondent and his head split into thousands of pieces. Amitabha Buddha put the pieces back together as a body with very many arms and many heads, so that Chenrezig could work with myriad beings all at the same time. Sometimes Chenrezig is visualized with eleven heads, and a thousand arms fanned out around him.