Guanyin
Guanyin, or Kwan Yin, is known as the bodhisattva of compassion, and the goddess of mercy in Eastern Asia. In some Buddhist teachings, a bodhisattva is one who has become enlightened enough to obtain nirvana, but instead decides to compassionately help others obtain enlightenment as well: Guanyin represents the compassion of the Buddha.
It is believed that Guanyin in Eastern Asian cultures is derived from Avalokitesvara, the Sanskrit name for this bodhisattva. Avalokitesvara is known solely as a bodhisattva, while Guanyin in East Asian cultures (such as China) is thought of as a goddess as well. Many stories and legends of Guanyin are different, and independent of the original Buddhist tellings. Manhy deal with how Guanyin came to be a bodhisattva or a goddess.
In Mahayana Buddhism, Avalokitesvara is thought to be able to transform into whatever gender or form, an ability that all bodhisattvas have. This is thought to better help others obtain enlightenment. Avalokitesvara is referred as a male being, however Guanyin is often referred to as a female, although the latter can be both male and female.