The Luo, (also spelled Lwo) are several ethnically and linguistically related Nilo-Semitic ethnic groups that inhabit an area ranging from Egypt and Sudan to South Sudan and Ethiopia, through Northern Uganda and eastern Congo (DRC), into western Kenya, and the Mara Region of Tanzania. Their Luo languages belong to the western branch of the Nilotic language family.
The Luo groups in South Sudan include the Shilluk, Anuak, Pari, Acholi, Balanda Boor, Thuri and Luwo. Those in Uganda include the Alur, Acholi, Jonam and Padhola. The ones in Kenya and Tanzania are the Joluo (also called Luo in Kenyan English).
The Joluo and their language Dholuo are also known as the "Luo proper" by Kenya based observers, even though their dialect has more Bantu loan words than the rest.
The level of historical separation between these groups is estimated at about eight centuries. Dispersion from an alleged Nilotic core region in South Sudan is presumed to have been triggered by the turmoil of the Muslim conquest of Sudan. The migration of individual groups over the last few centuries can to some extent be traced in the respective group's oral history.
The Luo are part of the Nilotic group of people. The Nilotes had separated from the other members of the East Sudanic family by about the 3rd millennium BC. Within Nilotic, Luo forms part of the Western group.
Within Luo, a Northern and a Southern group is distinguished. Dholuo is part of the Southern Luo group. Northern Luo is mostly spoken in South Sudan, while Southern Luo groups migrated south from the Bahr el Ghazal area in the early centuries of the second millennium AD (about eight hundred years ago).
A further division within the Northern Luo is recorded in a "widespread tradition" in Luo oral history: the foundational figure of the Shilluk (or Chollo) nation was a chief named Nyikango, dated to about the mid-15th century. After a quarrel with his brother, he moved northward along the Nile and established a feudal society. The Pari people descend from the group that rejected Nyikango.