Korea's Paekchong minority ethnicity is an "outcast" group, somewhat comparable to the untouchables of India, although in many ways they are more akin to Europe's gypsies (aka Roma), because they are made up of a population that made a mass migration to Korea, in the historic era, from abroad, but has retained an ethnic identity at society's fringes rather than integrating into society's mainstream. A similar underclass in Japan is called the Burakumin.
According to Korean historical sources, they have origins as several waves of tribes of nomadic people who primarily relied upon hunting, selling crafts and entertaining, the first wave of which arrived in Korea around 1217 CE. King Sejong (1419-1450) attempted to integrate them into Korean society, but this effort failed over the next five hundred years, until that integration was fairly fully effected after the Korean War. Instead, they eventually settled into a lifestyle on the fringe of Korean society in ghettos where they carried out slaughtering trades in additional to their traditional means of self-support.
A lengthy blog post provides a sentence of who these people are and where they came from historically, and muses on why it is (with genetic reasons among those considered) that this cultural legacy endured so long.
To the extent that Korea's Paekchong represent one of the late integrated hunter-gatherer populations of Northern Asia into Korean society, a study of their genetics just as the ethnicity is ceasing to be a cultural reality, could provide a time capsule of the genetics of such groups 800 years ago.