Which greek believed that power should be "not of a minority, but the whole people?

Pericles. The above quote is from a much larger piece of writing in which Pericles is delivering the eulogy for lost Athenian soldiers during the battle of Megaris. He continues to note that all should be equal in the eyes of the law, and that the needs of the many outweigh the needs of the few at length. The speech is documented in "History of the Peloponnesian War" by Thucydides.