Michael Bloomberg
He was a Democrat before running for office. He switched his party registration in 2001 to run for mayor as a Republican. He defeated opponent Mark Green in a close election held just weeks after the September 11 attacks. Bloomberg won a second term in 2005 and left the Republican Party two years later. He campaigned to change the city's term limits law and was elected to his third term in 2009 as an independent candidate on the Republican ballot line. He was criticized by many for his "Stop And Frisk" policy, which has been criticized for disproportionately affecting Black and Hispanic men in New York City, as most of those stopped (~90%) were not found to be guilty of any crime or wrongdoing.