If you visit a temple in Japan or any other Buddhist countries like China, Thailand, Korea, etc. you will find many different kinds and statues of deities. They are very artistic, sometimes mystic, and many people like to pray towards them. However, during the early stages in the Buddhist religion, which started in India, there were no statues of deities.
That is because Shakyamuni Buddha taught his followers “Make the Law (Dharma, or Buddhist teachings of Universal Truth) your light, and make the self your light”. So, it had been a taboo to make statues of him after his death for centuries.
He was one of the great enlighten spiritual teachers, but never wished to be worshipped as a god nor the “God”.
(It is believed that there had been six other teachers who had awaken to the truth before Shakamuni Buddha. )
Shakyamuni Buddha knew the risk of idle worship so clearly stated "You must not depend upon other people. You should also make the Dharma your light and depend on the Dharma. You must not depend upon others.”
As in the worldly famous proverb “God (Heven) helps those who helps themselves”, one should never forget to work on themselves for the awakening the Consciousness and to know the Truth by their own effort.
However, as Buddhism evolved in India centuries after Buddha’s death (1st century AD.) many Buddhist statues began to be made. They were used to represent deities described in the sutras and as visual objects of worship. Gradually, many statues of Shakamuni Buddha and his best disciples too.
In the 6th century (in 538), Buddhist statues , sutras and Buddha’s ashes were brought into Japan with the introduction of Buddhism. It became a state religion in Nara period.
Later in the history, Japanese Buddhism and styles of statues develops in its own way, different from the original forms with many influences from Shintoism, Chinese Taoism, etc. etc.
In Mahayana Buddhism, Buddhist statues are categories in 4 groups and each of them have quite clear features.
Nyorai (如来, Buddha)
Bosatsu (菩薩, Bodhisattva)
Myo-ou (明王, Vidyaraja)
Ten (天, Deva).