In the 1970s, Mr Lee worked in a glove factory as South Korea underwent a rapid economic rise.
A rarity among politicians in status-obsessed South Korea, former child factory worker Lee Jae-myung rose to become a presidential contender, telling voters his working-class roots equipped him to fight inequality.
Mr Lee, who was under treatment in Seoul after being stabbed in the neck on Tuesday, lost the tightest presidential election in South Korean history to Yoon Suk Yeol in 2022. The motive behind the attack was unknown.
Leading the country's main opposition party, Mr Lee has since been a staunch critic of President Yoon, and is widely expected to run for the top office again in 2027.
"I had to work in a factory because I couldn't pay for school," he told AFP before the 2022 election.
"My parents were cleaners. I escaped poverty, but many around me are still stuck... I want to change the system."
Mr Lee's political rise coincided with growing worries about inequality, sky-high housing prices and youth unemployment.
His time in elected office has been marked by policies including cash handouts to young adults, free school uniforms and free maternity care.
He has previously vowed to expand his universal basic income scheme nationwide as president.
While his supporters say these policies are rooted in Lee's own experience and empathy for the less fortunate, his opponents accuse him of being a populist who will pile on debt to pay for these schemes.
Mr Lee's journey up the ranks of South Korean politics has also been marred by scandal.
He faces trial on charges of bribery linked to a firm that is suspected of illicitly transferring $8 million to North Korea.
Mr Lee is also accused of a breach of duty that allegedly resulted in a loss of 20 billion won ($15 million) for a company owned by Seongnam city when he was its mayor.
Mr Lee avoided arrest in September last year when a court dismissed a prosecution request for him to be taken into custody pending trial on the various corruption charges.
The 59-year-old has denied all allegations against him.
Night school
In the 1970s, Mr Lee worked in a glove factory as South Korea underwent a rapid economic rise.
When he was 13, his arm got stuck in a press and he was left permanently disabled.
He then put himself through night school and a law school scholarship gave him a way out. Lee became a human rights lawyer before entering politics in 2010.
Although other politicians such as former president Roh Moo-hyun have grown up poor, South Korea's legislature is dominated by the wealthy and well-connected, with most parliamentarians classed as millionaires according to their declared assets.
In 2021, Mr Lee's presidential campaign attempted to hammer home the contrast between him and Yoon, who was raised in an affluent family.
They published two photographs: one showed a floppy-haired young Lee in an ill-fitting suit and the other a teenage Yoon in a bow tie.
Mr Lee's story resonated with a large swathe of South Korean voters but he lost the bitterly fought 2022 election by a razor-thin margin.
Recent polls have indicated that he remains a strong contender for the next presidential race in 2027.
He has, however, faced some calls from within his own party to step down as its leader ahead of legislative elections this year.