Buumi (many variations : Buumy, Bumy, Bumi, etc.) was a Serer royal title in the Serer pre-colonial 
Kingdoms of Sine, Saloum and previously Baol.  All these pre-colonial Serer kingdoms are now part of modern-day Senegal. However, present-day Gambia, was called Lower Saloum and a former colony of the Kingdom of Saloum. The Buumi was always a member of the royal family. He was the first in line to inherit the throne of the Maad a Sinig (King of Sine) or Maad Saloum (king of Saloum).  In some cases, a Buumi can act as regent if the king is too young, as was the case with Maad a Sinig Ama Joof Gnilane Faye Joof, whose uncle was appointed regent until Maad Ama Joof became much older. In pre-colonial Sine, the Buumi usually took residence at Somb Rongodior. In many cases, he was elected by the Maad a Sinig as his successor, however, the Great Jaraff and his Noble Council of Electors generally decides which member of the royal family succeeds to the throne.  When Maad a Sinig dies without nominating his Buumi, as was the case with Maad a Sinig Mbackeh Ndeb Njie, the "thilas" (the second in line to the throne) may succeed him as was the case with Maad a Sinig Kumba Ndoffene Fa Ndeb Joof.
 The Buumi was a very important figure in the Serer kingdoms. They had their own army and also led a contingent force of the country in times of war. At The Battle of Fandane-Thiouthioune (18 July 1867) also known as the Battle of Somb, the Buumi Somb commanded the army of eastern Sine.  In the Kingdom of Saloum, which had a very similar political structure as the Kingdom of Sine, the two most important Buumis were : the Buumi Kaymor (Buumi of Kaymor) and Buumi Mandak (Buumi of Mandak). They both took residence at Kaymor and Mandak (in Saloum), respectively. In Sine, there was also the Buumi Nguess (Buumi of Nguess) and Buumi Ndidor (Buumi of Ndidor).  Although they were all important figures, they should not be confused with the "Buumi" (their heir apparent). 
 Like the Serer title lamane, the Wolof have also adopted the Serer title buumi. One well known buumi of Jolof was Buumi Jeleen Yatta Ntanye (commonly known as Bumi Jelen, or D. João Bemoí, Bemoi, Bemohi, Bemoin, or Bemoim amongst the Portuguese, a corruption of the Serer term buumi). He was the 15th century Prince of Jolof who visited the King of Portugal João II in 1488 to help him sit on the throne of Jolof (then the Jolof Empire). The King of Portugal granted him military support and ships after his conversion to Catholicism but he was eventually assassinated by Pero Vaz da Cunha upon arriving at the mouth of the Senegal River. Pero Vaz was the very man the Portuguese King entrusted to protect Buumi Jeleen and oversea the mission and ensure Buumi Jeleen takes the throne of Jolof. Realising that he would remain in Jolof to oversea the conversion of the people and built a fort, and fearful of dying of disease, he assassinated Buumi Jeleen by stabbing him with a sword or dagger, before turning the ship around and returned back to Portugal, and falsely told the King of Portugal that Buumi Jeleen committed treason hence why he was killed.   Buumi Jeleen is the maternal half brother of the King of Jolof Buurba Jolof Biram Njemeh Eler Njie—who died in 1481 from suspicious circumstances. Yatta Ntanye is their mother. Biram Njemeh Eler is the direct ancestor of the Gambian historian, author, pan-Africanist, nationalist during the colonial era, and statesman Alhaji Alieu Ebrima Cham Joof. Cham Joof's paternal great grandmother - the Princess of Jolof Fa Kebbeh Njie, is a direct paternal descendant of Biram Njemeh Eler.