William Whittingham Lyman Jr. (January 3, 1885 – November 8, 1983), also known as Jack Lyman, was an American writer and academic, primarily in the field of Celtic studies.
Lyman was born at Napa County, California, the son of William Whittingham Lyman and Mrs Sarah A. Nowland, and the grandson of Theodore Benedict Lyman. His father built the Lyman winery, now known as the El Molino winery. In 1905, while an undergraduate at University of California, Berkeley, he was convinced by Charles Mills Gayley to achieve an academic major in English literature. Upon completion of his Master's degree, Gayley arranged for him to receive a university fellowship to travel to the University of Oxford to study Celtic languages with Sir John Rhys. After a year at Oxford, Lyman spent two years at Harvard University studying the Irish language. He returned to the University of California, Berkeley to take up a post as Instructor in Celtic (then a tenure-track position) within the English department in 1911-1912. In the same year, Celtic appears on the list of approved majors in the College of Letters and Science and in the following year Lyman is named also as "Graduate Adviser" in Celtic. There he remained until 1922, whereupon he moved to Southern California and taught English at Los Angeles City College until his retirement. After retirement he and his family moved back to the family home near the Bale Grist Mill north of St. Helena.