Traditional Buddhist beliefs do not include a god or goddess. How did Mahayana Buddhism develop to include many gods and goddesses?
As Buddhism developed and expanded, it incorporated beliefs and practices from the places it expanded into. For example, when Buddhism entered China, it found there already a pantheon of gods and goddesses. Some of these became part of the Buddhist faith as well, and these beings became known as Buddhas and bodhisattvas. They were regarded as enlightened beings who could help people achieve enlightenment. A goddess like the Chinese Guan-yin became the embodiment of the Buddhist virtue of Compassion; by praying to her, the Buddhist practitioner could advance toward nirvana. The same process happened in Japan where the local kami of Shinto became Buddhas and bodhisattvas. Mahayana included aspects of faith, so that a devout Buddhist could pray to a divine being for aid in the route to enlightenment. The most prominent example of this was the belief in Amitabha (in Japanese, "Amida"), a Buddha who was said to have created a Pure Land, a paradise where one could reach nirvana easily. One was reborn in the Pure Land by having faith, by calling on and praying to Amitabha.