Karl Nickerson Llewellyn (1893-1962) enrolled in the Law School after being wounded while serving as a volunteer in the German army in World War I. He was Editor-in-chief of the Law Journal 1918-19. After graduating in 1918 and receiving an advanced law degree (J.D.) in 1920, serving as an instructor at the Law School during his graduate study, Llewellyn returned to Yale in 1922 as a member of the faculty. He left Yale for Columbia after only three years, but his early Legal Realist work was to inform the rest of his career, particularly his contributions to the drafting of the Uniform Commercial Code.

With the possible exception of Jerome Frank, Llewellyn was the most prominent and important of the Yale Legal Realists of the 1920s and 1930s.