Simplify the following text for a Grade 9 native English-speaking person.
Original: Max Karl Ernst Ludwig Planck ( April 23 , 1858 -- October 4 , 1947 ) was a German physicist who is regarded as the founder of the quantum theory , for which he received the Nobel Prize in Physics in 1918 .
Simplified: Max Karl Ernst Ludwig Planck ( April 23 , 1858 in Kiel - October 4 , 1947 in GÃ ttingen ) was a physicist from Germany . He discovered quantum mechanics .