Pythagoras was born around 569 BC in Samos. His parents were Mnesarchus of Tyre, a traveling merchant, and Pythais of Samos. The story of how his parents met is quite simple. Mnesarchus went to Samos to sell some corn during a famine and met Pythais. They get married and have Pythagoras. Unbeknowest to them, Pythagorus will grow up to be one of the greatest mathematicians of all time.
Not much is known of Pythagoras' childhood years. It is known that he was well educated as a child. Some people say he ha older siblings, but that cannot be proven.
When Pythagoras was about twenty years old he went to see two very talented mathematicians, so that he could learn from them. these two mathematicians were Thales and Anaximander of Miletus. From them he learned much of his mathematical knowledge.
Pythagoras went to egypt around 535 BC to expand his knowledge and to start working on his own mathematic ideas.
Pythagoras was said to have started a secret coalition of mathematicians called the Brotherhood of Pythagoreans. They believed that the entire world and universe was controlled and ruled by numbers. It was within this time period that the Pythagorean Theorem was created. There was no real reason for creating this theorem. The brotherhood was just so centered around mathematics that they were trying to figure out the secrets of mathematics.
Link 1
Link 2