William Elliott Butler (born 20 October 1939) is a jurist and educator, the John Edward Fowler Distinguished Professor of Law, Dickinson School of Law, Pennsylvania State University (2005-) and Professorial Research Associate, School of Oriental and African Studies, University of London (2006-), and Emeritus Professor of Comparative Law in the University of London (2005-).
He is a pre-eminent authority on the legal systems of Russia, other members of the Commonwealth of Independent States (CIS), and Mongolia.
He is also extensively involved in the fields of public and private international law.Butler is a noted bibliophile and bookplate collector.
Married 1961 Darlene Mae Johnson (1939–1989), with two sons William III, (b.