Simplify the following text for a Grade 8 native English-speaking person.
Original: John Forbes Nash , Jr. ( born June 13 , 1928 ) is an American mathematician whose works in game theory , differential geometry , and partial differential equations have provided insight into the forces that govern chance and events inside complex systems in daily life .
Simplified: John Forbes Nash Jr. ( born June 13 , 1928 ) is an American mathematician who works in game theory and differential geometry .