William O'Dwyer (July 11, 1890 – November 24, 1964) was an Irish-American politician who served as the 100th Mayor of New York City, holding that office from 1946 to 1950.

In 1907, O'Dwyer began to study for the priesthood at the Pontifical University of Salamanca, a Jesuit seminary in Spain,[2] where he became fluent in Spanish.

He won election as the Kings County District Attorney in November 1939[4] and his prosecution of the organized crime syndicate known as Murder, Inc. made him a national celebrity.

[5] During that time, he was on leave from his elected position as district attorney and replaced by his chief assistant, Thomas Cradock Hughes, and was re-elected in November 1943.

At his inauguration, O'Dwyer celebrated to the song, "It's a Great Day for the Irish", and addressed the 700 people gathered in Council Chambers at City Hall: "It is our high purpose to devote our whole time, our whole energy to do good work...." He established the Office of City Construction Coordinator, appointing Park Commissioner Robert Moses to the post, worked to have the permanent home of the United Nations located in Manhattan, presided over the first billion-dollar New York City budget, created a traffic department and raised the subway fare from five cents to ten cents.

[6] Shortly after his re-election to the mayoralty in 1949, O'Dwyer was confronted with a police corruption scandal uncovered by the Kings County District Attorney, Miles McDonald.

He returned to New York City in 1951 to answer questions concerning his association with organized crime figures and the accusations followed him for the rest of his life.