Simplify the following text for a Grade 10 native English-speaking person.
Original: Conrad Gessner ( Konrad Gessner , Conrad GeÃ ner , Conrad von Gesner , Conradus Gesnerus , Conrad Gesner ; 26 March 1516 â `` 13 December 1565 ) was a Swiss naturalist and bibliographer .
Simplified: Conrad Gessner ( or Konrad Gessner , 26 March 1516 â `` 13 December 1565 ) was a Swiss naturalist and bibliographer .