Answer by taking a quote from the following article:

John Sidney McCain III (born August 29, 1936) is an American politician serving as the senior United States Senator from Arizona since 1987. He was the Republican nominee for President of the United States in the 2008 election, which he lost to Barack Obama. McCain graduated from the U.S. Naval Academy in 1958 and followed his father and grandfather--both four-star admirals--into the United States Navy. He became a naval aviator and flew ground-attack aircraft from aircraft carriers.

Various advocacy groups have given McCain scores or grades as to how well his votes align with the positions of each group. The American Conservative Union has awarded McCain a lifetime rating of 82 percent through 2015, while McCain has an average lifetime 12 percent "Liberal Quotient" from Americans for Democratic Action through 2015. CrowdPac, which rates politicians based on donations made and received, has given Senator McCain a score of 4.3C with 10C being the most conservative and 10L being the most liberal.  The non-partisan National Journal rates a Senator's votes by what percentage of the Senate voted more liberally than he or she, and what percentage more conservatively, in three policy areas: economic, social, and foreign. For 2005-2006 (as reported in the 2008 Almanac of American Politics), McCain's average ratings were as follows: economic policy: 59 percent conservative and 41 percent liberal; social policy: 54 percent conservative and 38 percent liberal; and foreign policy: 56 percent conservative and 43 percent liberal. In 2012, the National Journal gave McCain a composite score of 73% conservative and 27% liberal, while in 2013 he received a composite score of 60% conservative and 40% liberal.  Columnists such as Robert Robb and Matthew Continetti have used a formulation devised by William F. Buckley Jr. to describe McCain as "conservative" but not "a conservative", meaning that while McCain usually tends towards conservative positions, he is not "anchored by the philosophical tenets of modern American conservatism." Following his 2008 presidential election loss, McCain began adopting more orthodox conservative views; the magazine National Journal rated McCain along with seven of his colleagues as the "most conservative" Senators for 2010 and he achieved his first 100 percent rating from the American Conservative Union for that year. During Barack Obama's presidency, McCain was one of the top five Republicans most likely to vote with Obama's position on significant votes; McCain voted with Obama's position on such votes more than half the time in 2013 and was "censured by the Arizona Republican party for a so-called 'liberal' voting record."  From the late 1990s until 2008, McCain was a board member of Project Vote Smart which was set up by Richard Kimball, his 1986 Senate opponent. The project provides non-partisan information about the political positions of McCain and other candidates for political office. Additionally, McCain uses his Senate website to describe his political positions.

What year did he become senator?