As a confidant of the late President Roh Moo-hyun, Moon Jae-in symbolizes a yearning for the liberal rule of the past and a determination to win back power from the ruling conservative camp.
The 59-year-old human rights lawyer-turned-politician also represents the last remaining hope of the main opposition Democratic United Party (DUP) as it seeks to play its part in December's presidential election in the face of potential competition from the widely popular software entrepreneur-turned-professor Ahn Cheol-soo.
Ahn has said he will announce whether he will run as an opposition contender within a few days after the DUP's primary.
Born to a poor family in Geojae, South Gyeongsang Province in 1953, Moon entered Seoul's Kyunghee University as a major in law in 1972 after suffering extreme poverty through his middle and high school years.
Moon spent his college years at the forefront of a student movement opposing the dictatorship of then President Park Chung-hee, the late father of the ruling Saenuri Party's presidential candidate, Park Geun-hye.
He was arrested in 1975 while leading a student demonstration and pressed into the airborne forces after being expelled from university. The law major returned to school in 1980 and passed the second stage of the state bar exam, but was thrown back into prison on charges of violating martial law.
Moon later passed the final stage of the bar exam and tried to become a judge, but after being dropped due to his history of demonstrations, he returned to his hometown and joined a law firm.
It was during his years as a human rights lawyer that he met Roh, with whom he would spend the next 20-odd years as a trusted ally and colleague.
Moon served as the last chief of staff to Roh, from 2007-2008, after serving three terms as a senior presidential secretary in different departments.
He is currently serving his first term as a lawmaker after being elected in a district in the southeastern port city of Busan in April's general elections. (Yonhap)