Oisin (pronounced Usheen or Osheen) is a figure from Irish myth and legend, the son of Finn McCool (Finn mac Cumhail).
Sykes appropriated the name as a stand-in for R1b in his book,
Blood of the Isles.
Ruisko is a Basque given name. Oppenheimer used it for R1b in his book,
Origins of the British.
Both books are seriously outdated now.