Segal taught at Barnard College and was an expert in ancient history and semitic languages. Among his many important contributions to the field is his Two Powers in Heaven and Paul the Convert.
The following is a bio from his faculty page.
Alan F. Segal has academic degrees from the following institutions: Amherst College (B.A. 1967), Brandeis University (M.A. 1969), Hebrew Union College–Jewish Institute of Religion (B.H.L. 1971), and Yale University (M.A. 1971, M.Phil. 1973, Ph.D. 1975). Professor Segal's studies included English literature, psychology, anthropology, comparative religion, Judaica, Christian origins, and rabbinics. His publications include Two Powers in Heaven (Brill), Deus Ex Machina: Computers in the Humanities (Penn University Bulletin Board),Rebecca's Children: Judaism and Christianity in the Roman World (Harvard University Press), The Other Judaisms of Late Antiquity (Scholars Press) for the Brown University Judiaca Series, and Paul the Convert: The Apostasy and Apostolate of Saul of Tarsus (Yale University Press). In 2004 Professor Segal publishedLife After Death: A History of the Afterlife in Western Religions (Doubleday). He has published numerous articles and for a decade has been chair of the History of Religion Committee of the American Academy of Religion. He also serves on the editorial board of the Journal of Biblical Literature and has served in many official capacities both within the University and internationally.
Here is a short Wikipedia article about him.