John B. Anderson was a Republican U.S. Congressman from Illinois from 1961 to 1981, and ran for President of the United States as an independent candidate in 1980. He carried 5,719,850 popular votes, or 6.6% of the vote total, and no electoral votes.
Anderson originally intended to run in the Republican primary but ran as an independent instead after it became clear the party would coalesce around Ronald Reagan. He later debated Reagan during the presidential campaign, but the incumbent, Jimmy Carter refused to debate him. Anderson, a liberal Republican, ran his independent campaign slightly to the left of Jimmy Carter and had his strongest showing in New England and the Pacific Northwest, and his weakest showing in the Southeastern states. He was, indeed, an early RINO, who thought Reagan was too conservative and ran on a third party ticket after it was clear he wouldn't get the nomination.
He endorsed Barack Obama for President in 2008.