William Jason Morgan (born October 10, 1935 in Savannah, Georgia) is an American geophysicist who has made seminal contributions to the theory of plate tectonics and geodynamics. He is Knox Taylor Professor emeritus of geology and professor of geosciences at Princeton University.
After having received his BSc in physics from the Georgia Institute of Technology in 1957, he went to Princeton University, where he completed his PhD in 1964 under the supervision of Bob Dicke. He joined the faculty of the university immediately afterwards.
His first major contribution, made in the late 1960s, was to relate the magnetic anomalies of alternating polarity, which occur on the ocean bottom at both sides of a mid-ocean ridge, to seafloor spreading and plate tectonics.
From 1971 on he worked on the further development of the plume theory of Tuzo Wilson, which postulates the existence of roughly cylindrical convective upwellings in the Earth's mantle as an explanation of hotspots. Wilson originally applied the concept to Hawaii and explained the increase in age of the seamounts of the Hawaii-Emperor chain with increasing distance from the current hotspot location; however, the concept was subsequently applied to many other hotspots by Morgan and other scientists.
Morgan has received many honours and awards for his work, among them the Alfred Wegener Medal of the European Union of Geosciences (1983), the Maurice Ewing Award of the American Geophysical Union (1987), the Wollaston Medal of the Geological Society of London (1994) and the National Medal of Science of the USA, award year 2002.
"The theory of plate tectonics he published in 1968 is one of the major milestones of U.S. science in the 20th century," Anthony Dahlen, chair of the Princeton Department of Geosciences, wrote in 2003. 
"Essentially all of the research in solid-earth geophysical sciences in the past 30 to 35 years has been firmly grounded upon Jason Morgan's plate tectonic theory," Dahlen said. "The scientific careers of a generation of geologists and geophysicists have been founded upon his landmark 1968 paper."