Rex Andrew Sinquefield (/ˈsɪŋkfiːld/; born September 7, 1944) is an American businessman, investor, and philanthropist who has been called an "index-fund pioneer" for creating the first passively managed index fund open to the general public Sinquefield was also a co-founder of Dimensional Fund Advisors. He is active in Missouri politics; his two main interests being rolling back the income tax and increasing public funding for charter schools.