Complex sentence: Harry Clement Stubbs (May 30,1922-October 29,2003), better known by the pen name Hal Clement, was an American science fiction writer, widely considered to be a leader of the subgenre hard science fiction.
Split into simpler sentences: Harry Clement Stubbs (May 30,1922-October 29,2003), better known by the pen name Hal Clement, was an American science fiction writer. Clement is widely considered to be a leader of the subgenre hard science fiction.