“WE” have traced roots to William and are in The Doomsday Book. After/before that we have only a rough guess of where we may have ccme from. Most of us have dark blue eyes which origionated in north of Denmark, most likely Norse.
Before The Doomsday Book it was very difficult to trace parentage for more than a few generations. Going as far back as the 3rd century is a STRETCH!
As far as ancient "warrior kings" of Ireland, my own surname has legendary origins with such a king, in Co. Wicklow. But, it's just that, legendary. No proven line. No way whatsoever to prove it.
Sounds like somebody's been watching too much The Seeker.