Julius Wilford "Nicky" Arnstein (July 1879 – October 2, 1965) was an American professional gambler and con artist. Among his aliases were "Nick Arnold", "Nicholas Arnold", "Julius Arnold", "Wallace Ames", "John Adams", and "J. Willard Adair". He was best known as the second husband of Fanny Brice.
Arnstein was born in New Jersey. His father, Berlin-born Moses Arndstein, was a German Jew, and fought in the Franco-Prussian War. Nicky's mother, Thekla (Van Shaw), was Dutch. The couple raised their children in the Episcopal Church. First settling in New Jersey, the couple had two other children besides middle-child Nicky; son Louis (born 1877), and daughter Gesina (born 1883).
"Nicky" was short for nickel plate, a sobriquet bestowed in the 1890s when, as a boy, Arnstein rode a gleaming nickel-plated bicycle in the then-popular bike racing craze. However, he spent more time throwing races than winning them. He graduated to gambling on transatlantic liners and in European casinos, and eventually fell in with Arnold Rothstein, a loan shark, bookmaker, fence, Wall Street swindler, real estate speculator, and labor racketeer, who was best known for fixing the 1919 World Series.
In 1915, Arnstein was convicted of swindling, and the following year he entered Sing Sing to serve out his term. Fanny Brice visited him every week while he was there, and in 1918 Arnstein's wife Carrie sued her for alienation of his affection. She subsequently divorced him, leaving him free to marry Brice in October of that year.