Saint Cybi, or Cuby, was a 6th-century Cornish bishop, saint, and, briefly, king, who worked largely in Cornwall and North Wales: his biography is recorded in two slightly variant medieval 'lives'.

Rhyd-y-Saint railway station was situated on the Red Wharf Bay branch line between Holland Arms railway station and Benllech, the second station after the line branched from the main Anglesey Central