Rudolph William Louis Giuliani (/ˌdʒuːliˈɑːni/, Italian: [dʒuˈljaːni]; born May 28, 1944) is an American politician and disbarred lawyer who served as the 107th mayor of New York City from 1994 to 2001. He previously served as the U.S. associate attorney general from 1981 to 1983 and the U.S. attorney for the Southern District of New York from 1983 to 1989. Giuliani led the 1980s federal prosecution of New York City mafia bosses as U.S. attorney for the Southern District of New York. After a failed campaign for mayor of New York City in the 1989 election, he succeeded in 1993, and was reelected in 1997, campaigning on a "tough on crime" platform. He led New York's controversial "civic cleanup" from 1994 to 2001, and appointed William Bratton as New York City's new police commissioner. In 2000, he ran against First Lady Hillary Clinton for a U.S. Senate seat from New York, but left the race once diagnosed with prostate cancer. For his mayoral leadership following the September 11 attacks in 2001, he was called "America's mayor", and was named Time Person of the Year for 2001.

In 2002, Giuliani founded a security consulting business, Giuliani Partners, and acquired, but later sold, an investment banking firm, Giuliani Capital Advisors. In 2005, he joined a law firm, renamed Bracewell & Giuliani. Vying for the Republican Party's 2008 presidential nomination, Giuliani was an early frontrunner, yet did poorly in the primary election; he later withdrew and endorsed the party's subsequent nominee, John McCain. After declining to run for New York governor in 2010 and for the Republican presidential nomination in 2012, Giuliani turned his focus to his business firms. After advising Donald Trump during his 2016 presidential campaign and early administration, Giuliani joined President Trump's personal legal team in April 2018, remaining on it during the 2020 presidential election. His activities as Trump's attorney led to allegations that he engaged in corruption and profiteering. In 2019, Giuliani was a central figure in the Trump–Ukraine scandal.

Following the 2020 election, Giuliani represented Trump in many lawsuits filed in attempts to overturn the election results, making false and debunked allegations about rigged voting machines, polling place fraud, and an international communist conspiracy. Giuliani spoke at the rally preceding the January 6 United States Capitol attack, where he made false claims of voter fraud and called for "trial by combat". He was later also listed as an unindicted co-conspirator in the federal prosecution of Trump's alleged attempts to overturn the election. In August 2023, he was indicted in the prosecution related to the 2020 election in Georgia. Later in 2023, Giuliani lost a $148-million defamation lawsuit for his false claims about two election workers in Georgia, and unsuccessfully attempted to declare bankruptcy; he later reached a settlement to pay damages awarded to the election workers. In April 2024, he was indicted on charges related to the 2020 election in Arizona. He was later disbarred in the state of New York in July, and in the District of Columbia in September.

Giuliani was born on May 28, 1944, in the East Flatbush section of Brooklyn, New York City, which at the time of his birth was a largely Italian American enclave of Brooklyn. He is the only child of working-class parents Helen (née D'Avanzo) and Harold Angelo Giuliani, both children of Italian immigrants. Harold Giuliani, a plumber and a bartender, had trouble holding a job, was convicted of felony assault and robbery, and served prison time in Sing Sing. Once released, his father worked as an enforcer for his brother-in-law Leo D'Avanzo, who operated an organized crime-affiliated loan sharking and gambling ring from a restaurant in Brooklyn.

Giuliani was raised a Roman Catholic. When he was seven years old, his family moved from Brooklyn to Garden City South on Long Island, where he attended the local Catholic school, St. Anne's. Later, he commuted back to Brooklyn to attend Bishop Loughlin Memorial High School, where he graduated in 1961. Giuliani attended Manhattan College in Riverdale, Bronx, where he majored in political science with a minor in philosophy. Giuliani was elected president of his class in his sophomore year, but was not re-elected in his junior year. He joined the Phi Rho Pi college forensic fraternity and honor society. He graduated in 1965. Giuliani considered becoming a priest but decided to attend New York University School of Law in Manhattan, where he was a member of the New York University Law Review, and graduated cum laude with a Juris Doctor degree in 1968.

Giuliani started his career and political life as a Democrat, working as a Democratic Party committeeman on Long Island in the mid-1960s. In 1968, he volunteered for Robert F. Kennedy's campaign in the 1968 U.S. presidential election, and voted for George McGovern in the 1972 U.S. presidential election. After graduating from law school, Giuliani clerked for Judge Lloyd Francis MacMahon, U.S. district judge for the Southern District of New York.

Giuliani did not serve in the military during the Vietnam War. His conscription was deferred while he was enrolled at Manhattan College and NYU Law. Upon graduation from law school in 1968, he was classified 1-A (available for military service), but in 1969 he was reclassified 2-A (essential civilian) as Judge MacMahon's law clerk. In 1970, Giuliani was reclassified 1-A but received a high 308 draft lottery number and was not called up for service.

Giuliani switched his party registration from Democratic to independent in 1975. This occurred during a period of time in which he was recruited for a position in Washington, D.C., with the Ford administration. Giuliani served as the associate deputy attorney general and chief of staff to Deputy Attorney General Harold "Ace" Tyler.