Complex sentence: The Historical Society was founded on November 20,1804, largely through the efforts of John Pintard, who for some years was secretary of the American Academy of Fine Arts, as well as the founder of New York's first savings bank.
Split into simpler sentences: The Historical Society was founded on November 20,1804, largely through the efforts of John Pintard. He was for some years was secretary of the American Academy of Fine Arts, as well as the founder of New York's first savings bank.