Complex sentence: Harold Wallace Ross (November 6,1892--December 6,1951) was an American proprietary journalist who founded "The New Yorker" magazine, who served as editor-in-chief of the publication from it's inception in 1925 until his death.
Split into simpler sentences: Harold Wallace Ross (November 6,1892--December 6,1951) was an American proprietary journalist who founded "The New Yorker" magazine. He would serve as chief-editor of the publication from it's inception in 1925, to his death.