Simplify the following text for a Grade 8 native English-speaking person.
Original: Rudolf Christian Karl Diesel ( ; March 18 , 1858 â `` last seen alive September 29 , 1913 ) was a German inventor and mechanical engineer , famous for the invention of the diesel engine .
Simplified: Rudolf Christian Karl Diesel ( March 18 , 1858 â `` September 30 , 1913 ) was a German engineer and inventor . His best known invention is Diesel engine .