Many Koreans know him as the person who has always stood by the late President Roh Moo-hyun.
Whether during his time as a human rights lawyer, or serving as Roh's chief of staff, or even after President Roh took his own life in the village of Bongha, Moon Jae-in has stood by his longtime friend.
Moon and Roh first met in 1982, when Moon went to Busan to open a private practice.
But the two found that they had so much in common in terms of personality and professional goals, that they decided to go into practice together on the day they met.
That's how their lifelong friendship began.
After Roh was elected president in 2002, Moon supported him by serving as one of his top aides at the Blue House.
When the National Assembly attempted to impeach Roh on charges of illegal campaigning in 2004, Moon successfully defended him as his legal representative.
And in 2009, when President Roh fell from a cliff in an apparent suicide, Moon acted as his chief mourner, a position that is usually carried out by the eldest son of the deceased.
Moon entered politics this year when he won a seat in the National Assembly in the April general election, and later emerged as the presidential candidate for the main opposition Democratic United Party.
He has said that he never wanted to go into politics, as it didn't suit him, but added that he changed his mind because he could no longer ignore the need for political reform.
Moon is known for his principles, and President Roh once said that Moon was one of the most principled people he knew.
Moon was famous for not having had any private, off-the-record meetings with journalists during his term as Roh's chief of staff, as he didn't want Roh's policies misrepresented.
During his college years, Moon was arrested two times for fighting for his principles against the authoritarian rule of the administration of Park Chung-hee, whose daughter is now perhaps his biggest rival in this election.
Moon says that his dream as a politician is to narrow the socioeconomic gap in Korea, and become a president who responds to the needs of the underprivileged members of society.
Given his long history of partnership with Roh, he now faces the challenge of overcoming his image as "Roh Moo-hyun's shadow" and winning the hearts of the Korean people with his own vision and values.
Eoh Jin-joo, Arirang News.

Reporter : jjeoh@arirang.co.kr