Robert Seager II, 79, a historian and teacher, died July 21 at Fair Oaks Hospital hospice. He had heart disease.

Mr. Seager, a Reston resident, taught history at five universities and published several critically acclaimed biographies, one of which was nominated for the 1963 Pulitzer Prize.

Disciplined and deliberate, Mr. Seager was recognized for his irascible and witty classroom personality and the clarity of his writing. He said the most satisfying moment in teaching is to see a student "start to think."

During his 40-year career as a college professor, he admonished students to drop his class if they couldn't write or spell. "If a blue book comes back with real sentences, I'm so happy. It could be a recipe for fudge," he said, according to friends.

He was born in Nanjing, China, where his parents were missionaries. During World War II, Mr. Seager served in the Merchant Marine and received a diploma from its academy. He later received a bachelor's degree from Rutgers University, a master's degree from Columbia University and a doctoral degree from Ohio State University. He pursued postdoctoral studies at Johns Hopkins University. His areas of concentration included American, military and diplomatic history. He also served in the U.S. Naval Reserve.

Mr. Seager taught history at Denison University in Granville, Ohio, from 1949 to 1961, at the U.S. Naval Academy in Annapolis from 1961 1967, at the University of Maine from 1967 to 1970 and at Washington College in Chestertown, Md., from 1970 to 1972, where he also served as academic dean. From 1972 to 1977, he taught at the University of Baltimore, where he was vice president of academic affairs, and he taught at the University of Kentucky from 1977 until his retirement in 1987. He then moved back to the Washington area.

Among his awards were the U.S. Naval Institute Award of Merit, the Navy League Award for Literary Achievement, the North American Society for Oceanic History's John Lyman Book Award and the University of Kentucky Hallam Award, all for "Alfred Thayer Mahan: The Man and His Letters" (1977), a biography of the American naval strategist and historian.

Mr. Seager was the editor of "The Papers of Henry Clay" (1982) and "Henry Clay and John Tyler: Compromise and Conscience in the Old South, 1800-1861." He contributed articles and critical reviews to American Historical Review, The Washington Post, New England Quarterly and other publications.

Among Seager's published works, "And Tyler Too: A Biography of John and Julia Gardiner Tyler," (1963) was nominated for a Pulitzer.

His wife, Caroline Parrish Seager, died in 2003. His brother, Warren Armstrong Seager Jr., died in 1985.

He is survived by his companion, Judith E. Park of Reston.