Kingdom of Desmond in the context of Eóganacht Chaisil

Earl of Desmond (Irish: Iarla Dheasumhan meaning Earl of South Munster) is a title of nobility created by the English monarch in the peerage of Ireland. The title has been created four times. It was first awarded in 1329 to Maurice FitzGerald, 4th Baron Desmond, a Hiberno-Norman lord in Southwest Ireland, and it was held by his descendants until 1583 when they rose against the English crown in the Desmond Rebellions. Following two short-lived recreations of the title in the early 1600s, the title has been held since 1628 by the Feilding family of Warwickshire, England. The current holder is Alexander Feilding, 12th Earl of Denbigh and 11th Earl of Desmond (4th creation). The Earldom historically comprised what is now the entirety of County Limerick with large swathes of County Cork, County Kerry and County Waterford also being included. It bordered the Kingdom of Desmond, Kingdom of Thomond and the Earldom of Ormond

The Eóganachta (Modern Irish: Eoghanachta, pronounced [ˈoːnˠəxt̪ˠə]) were an Irish dynasty centred on Cashel which dominated southern Ireland (namely the Kingdom of Munster) from the 6/7th to the 10th centuries, and following that, in a restricted form, the Kingdom of Desmond, and its offshoot Carbery, to the late 16th century. By tradition the dynasty was founded by Conall Corc but named after his ancestor Éogan, the firstborn son of the semi-mythological 3rd-century king Ailill Aulom. This dynastic clan-name, for it was never in any sense a 'surname,' should more accurately be restricted to those branches of the royal house which descended from Conall Corc, who established Cashel as his royal seat in the late 5th century.

O'Sullivan (Irish: Ó Súilleabháin, Súileabhánach) is an Irish Gaelic clan based most prominently in what is today County Cork and County Kerry. According to traditional genealogy, the O’Sullivans were descended from the ancient Eóganacht Chaisil sept of Cenél Fíngin, the founder of the clan who was placed in the 9th century, eight generations removed from Fíngen mac Áedo Duib, king of Cashel or Munster from 601 to 618.Later, they became the chief princes underneath their close kinsmen, the MacCarthy dynasty, in the small but powerful Kingdom of Desmond, successor of Cashel/Munster.The last independent ruler of the clan was Donal Cam O'Sullivan Beare, who was defeated in the Nine Years' War of 1594–1603.