Omar Ahmed Khadr (Arabic: عمر أحمد خضر‎; born September 19, 1986) is a Canadian citizen convicted for war crimes under the United States Military Commissions Act of 2009, including murder in violation of the law of war and providing material support for terrorism. Khadr was tried by a Guantanamo military commission tribunal, a venue reserved for non-American enemy combatants captured in the War on Terror. In October 2010 he pleaded guilty to the five charges against him as part of a plea agreement with military commission prosecutors.

Khadr was captured on July 27, 2002 by American forces at the age of 15 following a four-hour firefight in the village of Ayub Kheyl, Afghanistan. As of May 2006, he was still detained in the Guantanamo Bay detention camp. Khadr signed a pre-trial agreement, pleading guilty to the charges, and the details of the charges and accepting an 8 year sentence, not including time served, with the possibility of a transfer to Canada after at least one year to serve the remainder of the sentence there, based on a US/Canada agreement.

In political jargon, useful idiot is a pejorative term used to describe people perceived as propagandists for a cause whose goals they do not understand, who are used cynically by the leaders of the cause.

The term was originally used to describe Soviet sympathizers in Western countries. The implication was that although the people in question naïvely thought of themselves as an ally of the Soviet Union, they were actually held in contempt and were being cynically used. The use of the term in political discourse has since been extended to other propagandists, especially those who are seen to unwittingly support a malignant cause which they naively believe to be a force for good.

An early usage identified is in a 1948 article in the social-democratic Italian paper L'Umanita - as cited in a New York Times article on Italian politics of the same year. Despite often being attributed to Lenin, in 1987, Grant Harris, senior reference librarian at the Library of Congress, declared that "We have not been able to identify this phrase among [Lenin's] published works."