Republican Senator Rand Paul has dropped out of the race for US president after a disappointing fifth place finish in the Iowa caucuses.
Mr Paul often clashed with his Republican rivals over their hawkish views on foreign policy and their support of government surveillance.
He ended his bid in part to focus on his re-election to the US Senate.
He is seen as representing the Libertarian wing of the party, which promotes individual rights and privacy.
“Across the country thousands upon thousands of people flocked to our message of limited government, privacy, criminal justice reform and a reasonable foreign policy,” he said.
“Although, today I will suspend my campaign for president, the fight is far from over.”
Mr Paul, an ophthalmologist, represents Kentucky in the US Senate and is the son of former Congressman Ron Paul, who ran for president several times.
He has said in the past he is the right candidate to “stand up to both the right and the left”.
Last year, a Time magazine cover labelled him “the most interesting man in politics”.
There are now 10 Republicans left in the White House race, down from the original 17.
The 52-year-old hoped to gain the attention of young people hoping for change but was ultimately overshadowed by billionaire businessman Donald Trump.
Mr Paul is known for holding up the Senate floor for nearly 13 hours to delay the nomination of John Brennan as CIA director because of his opposition to the Obama administration’s use of drone strikes against terrorists.
He also raised some eyebrows last year when he said vaccines could give children “profound mental disorders”. He later said his children are immunised.