| O'Sullivan Ó Súilleabháin | |
|---|---|
 Arms of O'Sullivan | |
| Parent house | Eóganachta |
| Country | Kingdom of Desmond Kingdom of Ireland |
| Founder | Suilebhan mac Maolura |
| Final ruler | Donal Cam O'Sullivan Beare |
| Titles |
|
| Cadet branches | O'Sullivan Mór O'Sullivan Beare O’Sullivan MacCragh MacCrohan McGillycuddy Labhrais-Clanlawrence |
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.