Sheikh Ahmed YassinYas·sin, Sheikh Ah·med /jæˈsiːn $ jɑː-, ˈɑːmed/ (1938–2004) a Palestinian man who was the leader of Hamas until he was killed by the Israelis. He started the Palestinian organization Hamas in 1987, together with Abdel Aziz al-Rantissi. The Israeli authorities sent him to prison for ordering the kidnapping and killing of two Israeli soldiers, but in 1997 they released him in exchange for two Israelis who were in prison in Jordan.