Muhammad Idris bin Muhammad al-Mahdi as-Senussi (Arabic: إدريس, romanized: Idrīs; 13 March 1890 – 25 May 1983) was a Libyan political and religious leader who was King of Libya from 24 December 1951 until his overthrow on 1 September 1969. He ruled over the United Kingdom of Libya from 1951 to 1963, after which the country became known as simply the Kingdom of Libya. Idris had served as Emir of Cyrenaica and Tripolitania from the 1920s until 1951. He was the chief of the Senussi Muslim order.

Idris was born into the Senussi Order. When his cousin Ahmed Sharif as-Senussi abdicated as leader of the Order, Idris took his position. The Senussi campaign was taking place, with the British and Italians fighting the Order. Idris put an end to the hostilities and, through the Modus vivendi of Acroma, abandoned Ottoman protection. Between 1919 and 1920, Italy recognized Senussi control over most of Cyrenaica in exchange for the recognition of Italian sovereignty by Idris. Idris then led his Order in an unsuccessful attempt to conquer the eastern part of the Tripolitanian Republic.

Following the Second World War, the United Nations General Assembly called for Libya to be granted independence. It established the United Kingdom of Libya through the unification of Cyrenaica, Tripolitania and Fezzan, appointing Idris to rule it as king. Wielding significant political influence in the impoverished country, he banned political parties and in 1963 replaced Libya's federal system with a unitary state. He established links to the Western powers, allowing the United Kingdom and United States to open military bases in the country in return for economic aid. After oil was discovered in Libya in 1959, he oversaw the emergence of a growing oil industry that rapidly aided economic growth. Idris' regime was weakened by growing Arab nationalist and Arab socialist sentiment in Libya as well as rising frustration at the country's high levels of corruption and close links with Western nations. While in Turkey for medical treatment, Idris was deposed in a 1969 coup d'état by army officers led by Muammar Gaddafi.