Rudolph William Louis "Rudy" Giuliani ( ; born May 28, 1944) is an American lawyer, businessman, and politician from the state of New York who was Mayor of New York City from 1994 to 2001.

A Democrat and Independent in the 1970s, and a Republican from the 1980s to the present, Giuliani served in the United States Attorney's Office for the Southern District of New York, eventually becoming U.S. Attorney. He prosecuted a number of high-profile cases, including ones against organized crime and Wall Street financiers.

Giuliani served two terms as Mayor of New York City. He was credited with initiating improvements in the city's quality of life and with a reduction in crime. Others, however, criticized him as divisive and authoritarian and disputed his role in reducing crime. He ran for the United States Senate in 2000 but withdrew due to being diagnosed with prostate cancer and to revelations about his personal life. Giuliani gained international attention during and after the September 11, 2001 attacks on the World Trade Center. In 2001, Time magazine named him "Person of the Year" and he received an honorary knighthood from Queen Elizabeth II in 2002.

After leaving office as mayor, Giuliani founded Giuliani Partners, a security consulting business; acquired Giuliani Capital Advisors (later sold), an investment banking firm; and joined the Bracewell & Giuliani law firm, which changed its name when he became a partner. Giuliani ran for the Republican Party nomination in the 2008 United States presidential election. After leading in national polls for much of 2007, his candidacy faltered late in the year and he did poorly in the early caucuses and primaries. He withdrew from the race in late January 2008.