Complex sentence: Henry Ellis (H.E.) Harris (January 21,1902--December 29,1977) was a philatelist and stamp dealer who through his company, H.E. Harris & Co., popularized philately for many Americans, especially children.
Split into simpler sentences: Henry Ellis (H.E.) Harris (January 21,1902--December 29,1977) was a philatelist and stamp dealer. Through his company, H.E. Harris & Co., Harris popularized philately for many Americans, especially children.