William Thomas Mulloy, Jr. (1917–1978) was an American anthropologist. While his early research established him as a formidable scholar and skillful fieldwork supervisor in the province of North American Plains archaeology, he is best known for his studies of Polynesian prehistory, especially his investigations into the production, transportation and erection of the monumental statuary on Rapa Nui (Easter Island) known as moai.
Mulloy was born May 3, 1917 in Salt Lake City, the only son of William Thomas Mulloy, Sr., a conductor on the Union Pacific Railroad, and Barbara Seinsoth Mulloy. His older sister, Mary Grace Mulloy Strauch, recognized and encouraged his early interest in archaeology. On the occasions of his childhood visits to her home in Mesa, Arizona, she would drive him to the town dump where he spent days at a time conducting his own stratification studies and enthusiastically reporting his results to her family at suppertime.
Mulloy earned a BA in anthropology from the University of Utah, where he had distinguished himself both in the classroom and on the wrestling team. From 1938 to 1939, he worked for the Louisiana State Archaeological Survey as a field archaeologist. In the Louisiana bayou, he contracted malaria. From Louisiana, Mulloy went to Illinois where he began graduate studies at the University of Chicago, then one of the world's foremost graduate schools of Anthropology and Archaeology. In the summer of 1940, Mulloy supervised archaeological fieldwork at Pueblo Bonito in Chaco Canyon, New Mexico. There, among the field crew, he met his future wife, Emily Ross, an archaeology major at the University of New Mexico.