During the battle between the real and fake Monkey Kings, Sun Wukong was killed by the combined forces of the Tathagata and Liu Er. Since his three souls and seven spirits were born of nature and had no place in the cycle of reincarnation, a spell scattered them across the Ten Directions Worlds.
One fragment of his soul fell onto a black bear in one of those worlds. But the black bear's own soul came from Earth... And so began the bear's journey to immortality.
