Isaiah is a major prophet in the Hebrew Bible, also known as the Old Testament. He was active during the 8th century BCE and is considered one of the four major prophets along with Jeremiah, Ezekiel, and Daniel. Isaiah is credited with writing the Book of Isaiah, which contains prophecies about the coming of the Messiah and the end of days. He is also credited with writing several other books in the Bible, including the Book of Micah and the Book of Habakkuk.