The Khalkha (/ˈkælkə, ˈkɑːlkə/; Mongolian: Халх ᠬᠠᠯᠬᠠ [ˈχa̠ɬχ]) have been the largest subgroup of the Mongols in modern Mongolia since the 15th century. The Khalkha, together with Chahars, Ordos and Tumed, were directly ruled by Borjigin khans until the 20th century. In contrast, the Oirats were ruled by Dzungar nobles and the Khorchins were ruled by Qasar's descendants.
The two original major Khalkha groups were ruled by the direct male line descendants of Dayan Khan. The Baarin, Khongirad, Jaruud, Bayaud and the O'zeed (Ujeed) became the subjects of Dayan Khan's fifth son Achibolod. They formed the Southern Five Halhs.