Thomas Edmund Dewey (March 24, 1902 – March 16, 1971) was an American lawyer and politician who served as the 47th governor of New York from 1943 to 1954. He was the Republican Party's nominee for president of the United States in 1944 and 1948, losing the former election to Franklin D. Roosevelt and the latter election to Harry S. Truman in a major upset.

As a New York City prosecutor and District Attorney in the 1930s and early 1940s, Dewey was relentless in his effort to curb the power of the American Mafia and of organized crime in general. Most famously, he successfully prosecuted Mafia boss Charles "Lucky" Luciano on charges of forced prostitution in 1936. Luciano was given a 30- to 50-year prison sentence. He also prosecuted and convicted Waxey Gordon, another prominent New York City gangster and bootlegger, on charges of tax evasion. Dewey almost succeeded in apprehending mobster Dutch Schultz as well, but Schultz was murdered in 1935, in a hit ordered by the Commission.

A progressive conservative, Dewey led the moderate faction of the Republican Party during the 1940s, and 1950s, in opposition to the more conservative Ohio Senator Robert A. Taft. Dewey was an advocate for the professional and business community of the Northeastern United States, which would later be called the Eastern Establishment. This group consisted of internationalists who were in favor of the United Nations, the New Deal reforms enacted during the administration of Democrat Franklin D. Roosevelt, and the fight against communism and the Soviet Union during the Cold War.

Dewey served as the 47th governor of New York from 1943 to 1954. In 1944, he was the Republican Party's nominee for the presidency, but lost the election to incumbent Franklin D. Roosevelt in the closest of Roosevelt's four presidential elections. Dewey won the Republican presidential nomination again in 1948; defeating Harold Stassen on his left and Robert A. Taft on his right. However, he lost to President Harry S. Truman in one of the greatest upsets in presidential election history. Dewey played a large role in winning the Republican presidential nomination for Dwight D. Eisenhower in 1952, helping Eisenhower win the presidential election that year. He also played a large part in the choice of Richard Nixon as the Republican vice-presidential nominee in 1952 and 1956. He was the first major party nominee to have been born in the 20th century.

Following his political retirement, Dewey served from 1955 to 1971 as a corporate lawyer and senior partner in his law firm Dewey Ballantine in New York City. In March 1971, while on a golfing vacation in Miami, Florida, he died from a heart attack. Following a public memorial ceremony at St. James' Episcopal Church in New York City, Dewey was buried in the town cemetery of Pawling, New York.

Dewey once described his career in public life as that of "a political engineer…a conservative facing up to the political facts of life."

Dewey was born and raised in Owosso, Michigan, where his father, George Martin Dewey, owned, edited, and published the local newspaper, the Owosso Times. His mother, Annie (Thomas), whom he called "Mater", bequeathed her son "a healthy respect for common sense and the average man or woman who possessed it". She also left "a headstrong assertiveness that many took for conceit, a set of small-town values never entirely erased by exposure to the sophisticated East, and a sense of proportion that moderated triumph and eased defeat". One journalist noted that as a boy "he did show leadership and ambition above the average; by the time he was thirteen, he had a crew of nine other youngsters working for him" selling newspapers and magazines in Owosso. In his senior year in high school he was the president of his class and the chief editor of the school yearbook. His senior caption in the yearbook stated "First in the council hall to steer the state, and ever foremost in a tongue debate", and a biographer wrote that "the bent of his mind, from his earliest days, was towards debate". He received his B.A. degree from the University of Michigan in 1923, and his LL.B. degree from Columbia Law School in 1925.

While at the University of Michigan, Dewey joined Phi Mu Alpha Sinfonia, a national fraternity for men of music, and was a member of the Men's Glee Club. While growing up in Owosso he was a member of the choir at Christ Episcopal Church. He had a deep, baritone voice, and in 1923 he finished in third place in the National Singing Contest. He briefly considered a career as a professional singer but decided against it after a temporary throat ailment convinced him that such a career would be risky. He then decided to pursue a career as a lawyer. He also wrote for The Michigan Daily, the university's student newspaper.