Question

Why did Gautama Buddha came to be called the Buddha?

Answer 1

Siddhartha Gautam attains enlightenment after meditating under the bodhi tree. He was called Buddha which means the "enlightenment one" or "awakened one".

The monks did not believe him to be a God but an awakened man who sees the truth behind everything.

Buddhist legend tells that at first, the Buddha was happy to dwell within this state, but Brahma, king of the gods, asked, on behalf of the whole world, that he should share his understanding with others. 

Answer 2

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By finding the path to Enlightenment, Siddhartha was led from the pain of suffering and rebirth towards the path of Enlightenment and became known as the Buddha or 'awakened one'.