There are also stories of him at Caer-Gynyr (later Caer Cai) near Bala in Penllyn and it was at these fortified sites, according to legend, that he raised the High-King Arthur as his foster-son. This followed Myrddin (alias Merlin)'s agreement with the High-King Uther that his son should be brought up free from the knowledge of his onerous inheritance, with the magician as his tutor. In later romance, Cynyr became known as Sir Ector.

Cynyr is occasionally called Cynyr Wledig (the Imperator) or Cynyr Goch (the Red). His Christian name is the equivalent of the Irish, Connor, and indicates that he was one of the many Irish immigrants who are known to have colonized Dyfed in the mid-5th century. He should probbaly be identified with Prince Conchrad (son of Duí Tenga Uma, a late 5th century King of Connaught) who was St. Mo-Chop (Cybi)'s grandfather.

Cynyr apparently married a lady named Sefin, possibly a daughter of St. Brychan, King of Brycheiniog, a monarch also of Irish origin. She appears in old Welsh poetry as the mother of Cynyr's son, Cai Hir. The mother of his other children appears to have been a second wife called Anna, perhaps the daughter of Vortimer Fendigaid, King of Gwerthefyriwg (Gwent).

Records of Cynyr date back to the 11th century. He could be historic but is is generally considered apocryphal.