Simplify the following text for a Grade 10 native English-speaking person.
Original: Sheikh Ahmed Ismail Hassan Yassin ( 1937 â `` 22 March 2004 ) was a founder of Hamas , an Islamist Palestinian paramilitary organization and political party . Yassin also served as the spiritual leader of the organization .
Simplified: Ahmed Yassin ( January 1 , 1929 â `` March 22 , 2004 ) was a spiritual leader of the militant Palestinian group Hamas .