Simplify the following text for a Grade 9 native English-speaking person.
Original: Martin Heidegger ( September 26 , 1889 â `` May 26 , 1976 ; ) was an influential German philosopher known for his existential and phenomenological explorations of the `` question of Being . ''
Simplified: Martin Heidegger ( September 26 , 1889 â `` May 26 , 1976 ) was a German philosopher .