Sheikh Ahmed Ismail Hassan Yassin (1937 – 22 March 2004) (Arabic: الشيخ أحمد إسماعيل ياسين‎) was a founder of Hamas, a Palestinian paramilitary organization and political party. Yassin also served as the spiritual leader of the organization. Hamas gained popularity in Palestinian society by establishing hospitals, education systems, libraries and other services, but it has also claimed responsibility for a number of suicide attacks targeting Israeli civilians, leading to its being characterized by a number of western states as a terrorist organization.

Yassin, a paraplegic who was nearly blind, had been confined to a wheelchair since a sporting accident at the age of 12. He was assassinated by an Israeli pilot of an helicopter gunship in 2004. His killing, in an attack that claimed the lives of as many as nine bystanders, precipitated much criticism of Israel, and many observers suggested that the act would negatively impact the peace process. 200,000 Palestinians attended his funeral procession.

Ahmed Yassin was born in al-Jura, a small village near the city of Ashkelon, during the British Mandate of Palestine. His date of birth is not known for certain: according to his Palestinian passport, he was born on 1 January 1929, but he claimed to have actually been born in 1938. His father, Abdullah Yassin, died when he was three years old. Afterward, he became known in his neighborhood as Ahmad Sa'ada after his mother Sa'ada al-Habeel. This was to differentiate him from the children of his father's other three wives. Together, Yassin had four brothers and two sisters. He and his entire family fled to Gaza, settling in al-Shati Camp after his village was captured by the Israel Defence Forces during the 1948 Arab–Israeli War.