Here is a comprehensive summary of the Wikipedia article about Lindsey Olin Graham:

Lindsey Olin Graham, born July 9, 1955, is an American politician and attorney currently serving as the senior U.S. Senator from South Carolina since 2003, representing the Republican Party. He had a distinguished military career, retiring as a Colonel from the Air Force Reserve in 2015 after serving in the Judge Advocate General's Corps as a defense attorney and chief prosecutor in Europe, earning a Bronze Star Medal in 2014. Before his Senate tenure, Graham served in both the South Carolina House of Representatives (1993-1995) and the U.S. House of Representatives (1995-2003).

Initially known as a neoconservative and defense hawk willing to work with Democrats on issues like immigration reform, he also sought the Republican presidential nomination in 2015. Notably, after being an outspoken critic of Donald Trump's 2016 candidacy, especially concerning his close friend John McCain, Graham became a staunch Trump ally following a March 2017 meeting, a significant reversal that garnered media attention.