From the Hebrew name Yesha'yahu meaning "Yahweh is salvation", from the roots yasha meaning "to save" and yah referring to the Hebrew God. Isaiah is one of the four major prophets of the Old Testament, supposedly the author of the Book of Isaiah. He was from Jerusalem and probably lived in the 8th century BC, at a time when Assyria threatened the Kingdom of Judah. As an English Christian name, Isaiah was first used after the Protestant Reformation.Jewish prophet.