John Marshall was the 4th Chief Justice of the US, and perhaps the most important, as his decision in Marbury v Madison birthed the philosophy of "judicial review." In other words, not until Marbury v Madison did SCOTUS have the ability to declare laws unconstitutional. Before this decision, SCOTUS essentially couldn't strike down laws passed by the Congress as unconstitutional, because prior to this decision the Constitution was not considered law, but just a statement of principles.