Rashid ad-Din Sinan, also known as The Old Man of the Mountain (c. 1132/1135 – 1192), was a leader of the Ismaili religious sect (Nizari branch) in Syria, and a figure in the history of the Crusades.

Latin sources from the Crusader states call him Vetulus de Montanis, derived from the Arabic title Shaykh al Jabal, which means "wise man or elder of the mountain".