Yoon was a relative newcomer to politics when he won the presidency. He had risen to national prominence for prosecuting the corruption case against disgraced former President Park Geun-hye in 2016.
In 2022, the political novice narrowly beat his liberal opponent Lee Jae-myung by less than 1% of the vote - the closest result the country has seen since direct elections started to be held in 1987.
At a time when South Korean society was grappling with widening divisions over gender issues, Yoon appealed to young male voters by running on an anti-feminism platform.
He has championed a hawkish stance on North Korea. The communist state was cited by Yoon on Tuesday night when he announced martial law.
He said he needed to protect against North Korean forces and “eliminate anti-state elements”, even though it was apparent from the outset that his announcement was less about the threat from the North and more about his domestic woes.
Yoon has had some success in foreign policy, notably improving ties in the the fraught relationship with Japan.
Yoon is known for gaffes, which haven’t helped his ratings. During his 2022 campaign he had to walk back a comment that authoritarian president Chun Doo-hwan, who declared martial law and was responsible for massacring protestors in 1980, had been "good at politics".
Later that year he was forced to deny insulting the US Congress in remarks made after meeting US President Joe Biden in New York.
He was caught on a hot mic and seen on camera seemingly calling US lawmakers a Korean word that can be translated as "idiots" or something much stronger. The footage quickly went viral in South Korea.