Complex sentence: A Fomrer Slave who turned royal guard and detective of King Sejong (whom he held a grudge against) as a child, Ddol-Bok protected his mentally-retarded father from the teasing of other servants of the Queen's family.
Split into simpler sentences: A Fomrer Slave who turned royal guard and detective of King Sejong (whom he held a grudge against). As a child, Ddol-Bok protected his mentally retarded father from the teasing of other servants of the Queen's family.