John Riordan

John Riordan may refer to:


 * John Riordan (mathematician) (1903–1988), American mathematician
 * John Riordan (banker), American banker, "Oskar Schindler of the Vietnam War"
 * John R. Riordan (born 1943), Canadian biochemist
 * John Riordan (businessman), Canadian businessman, owner of Riordon Paper Mills and The Toronto Mail (from 1877 to 1895)
 * John Riordan (jockey) (1936–2021), New Zealand jockey