(St.) or St. Regulus, a monk of Patrae in Achaia, is the real saint of Scotland. He was the first to colonise its metropolitan see, and to convert the inhabitants (370). The name Killrule (Cella Reguli) perpetuates this fact. St. Andrew superseded the Achaean.
But I have solemn vows to pay. ... To far St. Andrew's bound, Within the ocean-cave to pray, Where good St. Rule his holy lay Sung to the billow's sound.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894