Khalka Mongols
Khalkha (Mongol: Халх, lit. "the Shield") is the largest subgroup of Mongol people in Mongolia since 15th century. The Khalkha together with Tsahar, Ordos and Tumed, were directly ruled by the Chinggisid Khans until the 20th century; unlike the Oirat people who were ruled by the Dzungar nobles or the Khorchins who were ruled by Khasar's descendants. There were originally two major Khalkha groups, of which each ruled by the direct male line descendants of Dayan Khan. The Baarin, Qongirat, Jaarut, Baigut, and the O'zeed became Dayan Khan's fifth son Achibolod's subjects, thus formed the Southern Five Halhs. The Kerait, Jalair, Olkhunut, Khatagin, Besut, Iljigin, Gorlos, Uriankhai, Sartuul, Tanghut, Khotogoid, Khuree, and Tsookhor became Dayan Khan's youngest (could be third) son Geresenje's (Mongolian: Гэрсэне Жалайр Хан) subjects, thus formed the "Аглагийн арван гурван хүрээ Халх" or The Thirteen Khalkhas of the Far North. There were also numerous direct descendants of Genghis Khan who had formed the ruling class of the Khalkha Mongols prior to the 20th century, but they were and still also regarded as Khalkha Mongols rather than belonging to a special unit. The Thirteen Khalkhas of the Far North are the major subethnic group of the independent state of Mongolia. They number 1,610,400, or 78.8 percent, of Mongolia's population (1989 figures). Khalkha dialect is the standard written language of Mongolia.
Read more about Khalka Mongols: Etymology, History, Khalkha Diaspora, Loss of Khalkha Territory To Imperial Russia and The Buriatized Khalkhas