O'Sullivan clan descended from the followers of Milesius who were the
first Celts to colonize Innisfail, their "island of destiny". They had
migrated from an area of the northwest coast of Spain which is now known
as the province of Galicia. There they had founded a city they called
Brigantia. They had remained there for several generations before
embarking on the last leg of their odyssey. They arrived in their promised
land in approximately the year 800 B.C. They conquered the people that
were there at that time, the Firbolg and the Tuatha de Dannan.
Irish language O'Sullivan is O'Suilleabhain. Language experts suggest that
it means one-eyed or hawk-eyed. Suilleabhain was a direct descendant of
Finghin who was a king of Munster in the year 620 A.D. Suilleabhain was
born 8 generations later which would place him in the year 862.