A renowned Goryeo general who repelled the great Mongol army at Gwiju Fortress
| Era | 고려 |
| Clan | 죽산 박씨 |
Bak Seo of the Juksan Bak clan was the son of Bak In-seok, who had earned merit suppressing a Silla-restoration uprising in 1202; Bak Seo was the youngest of his ten children. As military commissioner of the northwestern frontier in 1231, he faced the first Mongol invasion led by Sartai.
Together with Kim Gyeong-son and Kim Jung-on, he held Gwiju Fortress for over a month against relentless Mongol siege engines, tying down more than 10,000 troops — over a third of the Mongol expeditionary force — for four months, buying time for the rest of Goryeo to prepare its defenses in what is remembered as one of Goryeo's most heroic stands against the invasion.
Under pressure from the royal court during subsequent peace negotiations he surrendered, and changed his name to Bak Mun-seong to evade Mongol reprisal before returning to office, eventually rising to Munha pyeongjangsa; little is recorded of his later life or death. In 2010, Korea's War Memorial named him a Hero of the Month.
His descendants formed the Goseong Park clan for a time before restoring their ancestral seat to the Juksan Park clan in 1839.