Nathan Freudenthal Leopold Jr., American murderer (b. 1904)
Nathan Freudenthal Leopold Jr. (November 19, 1904 – August 29, 1971) and Richard Albert Loeb (; June 11, 1905 – January 28, 1936), usually referred to collectively as Leopold and Loeb, were two wealthy students at the University of Chicago who kidnapped and murdered 14-year-old Bobby Franks in Chicago, Illinois in May 1924. They committed the murder – characterized at the time as "the crime of the century" – as a demonstration of their ostensible intellectual superiority, which they believed enabled and entitled them to carry out a "perfect crime" without consequences.

After the two men were arrested, Loeb's family retained Clarence Darrow as lead counsel for their defense. Darrow's 12-hour summation at their sentencing hearing is noted for its influential criticism of capital punishment as retributive rather than transformative justice. Both young men were sentenced to life imprisonment plus 99 years. Loeb was murdered by a fellow prisoner in 1936; Leopold was released on parole in 1958.

The Franks murder has been the inspiration for several dramatic works, including Patrick Hamilton's 1929 play Rope and Alfred Hitchcock's 1948 film of the same name. Other films based on the crime included Compulsion (1959), adapted from Meyer Levin's 1957 novel; Swoon (1992); and Murder by Numbers (2002). Scream (1996) writer Kevin Williamson confirmed in an interview with online publication Pride Source that the film's iconic murderers Billy Loomis and Stu Macher were also based on Leopold and Loeb.