(The). He calls himself (1) Head of the Catholic or Universal Church; (2) Sole Arbiter of its Rights; and (3) Sovereign Father of all the kings of the earth. From these assumptions he wears a triple crown- one as High Priest, one as Emperor, and one as King. (See Brady, 250, 251.)
For the first five centuries the Bishops of Rome wore a bonnet, like other ecclesiastics. Pope Hormasdas (514-523) placed on his bonnet the crown sent him by Clovis.
Boniface VIII. (1224-1303) added a second crown during his struggles with Philip the Fair. John XXII. (1410-1415) assumed the third crown.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894