American businessman and politician, who founded a financial data-services firm and served as mayor of New York City (2002– ).

His father, a Polish immigrant, was a bookkeeper and his mother was a secretary. After studying engineering at Johns Hopkins University (B.S., 1964), he attended Harvard University (M.B.A., 1966) and took an entry-level position with Salomon Brothers investment bank. Within 15 years he had achieved the level of partner and was leading the firm's block trading operations. When Salomon's acquisition by another firm in 1981 left him without a job, Bloomberg's $10 million partnership buyout provided the funding he needed to create Innovative Market Systems, a financial-data service firm, in 1982. Twenty years later, the renamed Bloomberg LP had become a global leader in financial data services. Central to the company's success was the Bloomberg computer terminal, a comprehensive financial news and information source. The company's other holdings included the Bloomberg Business News wire service, news radio station WBBR in New York City, and Bloomberg Television.

While at the helm of his company, Bloomberg served on the boards of leading cultural institutions, including the Metropolitan Museum of Art, Lincoln Center for the Performing Arts, the Central Park Conservancy, and the Jewish Museum, and he donated $100 million to Johns Hopkins University. Yet he had been known for tyrannical outbursts in the Bloomberg offices, browbeating employees and turning against anyone who left his firm. Intensely competitive, Bloomberg, a lifelong Democrat, entered the 2001 race for mayor of New York City—as a Republican. Bloomberg funded much of his mayoral campaign himself, spending more than $68 million from his personal fortune (his reported net worth at the time was roughly $4.5 billion).

His campaign themes focused on issues of great concern to New Yorkers: improvements in traffic and transit, housing, and education. What helped him most, however, was the endorsement of outgoing New York City Mayor Rudolph Giuliani (Giuliani, Rudolph W.), whose leadership following the September 11 attacks was universally praised. After trailing badly in the polls just weeks before the November 6 election, Bloomberg won the mayor's race. He immediately led redevelopment efforts, pushed for the passage of a controversial citywide smoking ban (the Smoke-Free Air Act of 2002), revitalized tourism, and erased the city's budget deficit. Elected to a second mayoral term in 2005, Bloomberg promoted a ban on trans fat in foods, pursued environmental initiatives such as congestion pricing during peak traffic hours, and proposed a 25-year plan for improving the city's infrastructure. He also raised his national profile by delivering policy-related speeches around the country and, in 2007, withdrawing from the Republican Party, all of which fueled rumours of Bloomberg's interest in a 2008 U.S. presidential bid as an independent candidate. Instead, however, he announced in October 2008 that he would seek reelection as mayor if the term-limit law were amended; several weeks later the New York City Council revised the law to allow three consecutive terms.