Simplify the following text for a Grade 7 native English-speaking person.
Original: Duke Nukem 3D features the adventures of the titular macho Duke Nukem ( voiced by Jon St. John ) , who fights back an alien invasion on Earth .
Simplified: Duke Nukem 3D is based on the main character from the platform games Duke Nukem and Duke Nukem II which were also published by Apogee . The character is voiced by Jon St. John .