John "Knickerbocker" Reiff (1885–1974) was an American flat racing jockey, whose greatest successes came in Great Britain where he won three Classics.

[1] At the time, he weighed just over 5 stone and gained the nickname "Knickerbocker" because of his juvenile style of dress.

[3] As a result of this incident, the younger Reiff moved to France, where, for a time he had his licence rescinded for the same reason.

Reiff still returned to England for big races and the trips brought his biggest successes.

He did win the 2000 Guineas that year on Louvois, although ironically many present believed Craganour actually won the race and the judge had called it incorrectly.