Michael Rubens "Mike" Bloomberg (born February 14, 1942) is an American businessman, author, politician, and philanthropist. His net worth is estimated at US$ 50.4 billion, as of June 2017, ranking him as the 6th richest person in the United States and the 8th richest person in the world. He has joined The Giving Pledge, whereby billionaires pledge to give away at least half of their wealth. Bloomberg is the founder, CEO, and owner of Bloomberg L.P., a global financial services, mass media, and software company that bears his name, and is notable for its Bloomberg Terminal, a computer software system providing financial data widely used in the global financial services industry. He began his career at the securities brokerage Salomon Brothers, before forming his own company in 1981 and spending the next twenty years as its chairman and CEO. Bloomberg also served as chairman of the board of trustees at his alma mater, Johns Hopkins University, from 1996 to 2002. Bloomberg served as the 108th Mayor of New York City, holding office for three consecutive terms, beginning with his first election in 2001. A Democrat before seeking elective office, Bloomberg 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 terrorist attacks. He won a second term in 2005, and left the Republican Party two years later. Bloomberg 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. Bloomberg was frequently mentioned as a possible candidate for the U.S. Presidential elections in 2008, and 2012, as well as for Governor of New York in 2010. He declined to seek either office, opting to continue serving as the Mayor of New York City. On January 1, 2014, Bill de Blasio succeeded Bloomberg as the Mayor of New York City. After a brief stint as a full-time philanthropist, Bloomberg re-assumed the position of CEO at Bloomberg L.P. by the end of 2014. On March 7, 2016, Bloomberg announced that he would not run as a third party candidate in the 2016 U.S. presidential election despite widespread speculation that he would, and later endorsed Democratic nominee Hillary Clinton for president.