Why is Herodotus famous?

because he was the king

Umm... Not quite. Thucydides was a General in the war, in control of 7 ships. He was blamed for the loss of one of the cities and while in exile, he wrote The History of the Peloponnesian War. He was one of the first real historians, using information derrived from both sides of the war, and did not include anything religious. So he was one of the first to write a real history, instead of a religious story to explain what happened.