Jack Dreyfus, American businessman, founded the Dreyfus Corporation (d. 2009)
John J. Dreyfus, Jr. (August 28, 1913 – March 27, 2009) was an American financial expert and the founder of the Dreyfus Funds.

Born in Montgomery, Alabama, Dreyfus was a graduate of Lehigh University in Pennsylvania. He is widely publicized for being the man who "invented" the commonplace mutual fund through direct marketing to the public.His early television commercials featuring a lion emerging from the Wall Street subway station were successful.

According to Barron's Magazine end of Century issue, Jack Dreyfus was considered the 2nd most significant money manager of the last century.

Dreyfus married in 1939 Joan Personette, from whom he was divorced; they had one child, John (Jonny).

His paternal grandfather was a first cousin of Alfred Dreyfus, the protagonist of the French 19th-century anti-Semitic scandal known as the Dreyfus affair.

Jack Dreyfus was also a renowned championship bridge player.

In addition to this, Dreyfus also became something of a public activist and proponent for the use of Phenytoin, an anticonvulsant, for the treatment of several mental health disorders; Dreyfus was not a doctor but claimed that the drug, which was prescribed to him in 1966, had alleviated his depression and chronic anxiety; after this, Dreyfus became a very vocal proponent for the research and clinical use of Phenytoin in these and other mental health diseases. Dreyfus would author a book titled A Remarkable Medicine Has Been Overlooked which he published and distributed with his own money (spending up to $70 million USD) and had the book sent for free to hundreds of doctors.In his role as a Phenytoin proponent, Dreyfus is known to have recommended the drug to Richard Nixon and it has also been claimed that on at least two occasions Dreyfus provided thousands of Phenytoin pills to him during his presidency to be used a sedative and antidepressant after Dreyfus profusely praised the drug while he dined in Bebe Rebozo's compound with Nixon who, intrigued, supposedly asked Dreyfus for pills who complied. This is a claim that was most prominently raised by Irish journalist Anthony Summers who published an unauthorized biography of Nixon titled Arrogance of Power: The Secret World of Richard Nixon in 2001 in which he raised these allegations; however, the claims that Dreyfus provided Nixon with Phenytoin who consumed them while in office have been fiercely disputed by historians and former colleagues of Nixon.Jack Dreyfus wrote and published his autobiography titled The Two Lives of Jack Dreyfus--The Lion of Wall Street published for the first time in 1995. He was a proponent of Phenytoin all his life and he also had his autobiography bound together with his previous work, A Remarkable Medicine Has Been Overlooked. This single volume containing both works, he distributed for free.John "Jack" Dreyfus died on March 27, 2009.