Oisín

A warrior-bard. Oisín (Oisin) was the son of Finn Mac Cumhaill and Sadb (Saba or Blaí), the woman-hind. See Sadb and the Birth of Oisín in the Fenian Cycle.

One tale tells of how he and Caílte Mac Ronan survived the Battle of Gabhra, in the Acallam na Senórach ("Colloquy of the Ancients"). Oisín parted company with Caílte, but later met his companion in Tara, where he also encountered St Patrick. Caílte and Oisín reminisced about a number of adventures of the Fian warrior, particularly ones about Finn.

In another tale, Oisín survived the Battle of Gabhra and met St Patrick, 300 years later. A beautiful Danann woman named Niam of the Golden Hair had lured Oisín to the Otherworld. They became lovers.

Later, when he decided to return to the surface, Niam warned him to not set foot on the surface, but to remain mounted on a magical horse. He broke this geis, and was transformed into an old man. Oisin discovered that all his companions had been dead for three hundred years.

Oisín then met St Patrick, where he told the saint of his life with his father (Finn) and the adventures of the Fianna. Several adventures were also recounted that he had in the Otherworld. Patrick had Oisin's tales recorded. Before the hero died, he was baptised.

It was Oisín who found the horn borabu under the rock. The borabu was sounded to summon Fian warriors from all parts of Ireland.