It was the famous Wellhausen hypothesis, elaborated and defended in his classic 'Prolegomena to the History of Ancient Israel', which more than any other single work of the mind revolutionized the critical understanding of the Hebrew Bible.
Prior to the appearance of Wellhausen, the theory proposed by Graf had been all but neglected. In it Graf had argued that the Levitical Law and related sections of the Pentateuch were not written until the fall of the kingdom of Judah, and that the Pentateuch in its present form was not accepted as authoritative until the reformation of Ezra. With Wellhausen's brilliant analysis of the literature and penetrating consideration of the sources, the Graf theory was accepted. Although today Wellhausen has been modified and revised, the development of contemporary Biblical criticism owes its present vitality and scope to the pioneering investigations of Wellhausen.
Julius Wellhausen (1844-1918). One of the most important biblical scholars of the 19th century, Wellhausen was particularly known for his work on the sources of the Hexateuch and his studies in Christian origins