This St. Peter is known as Peter the Exorcist. From very early times "exorcists" were men ordained to the ministry of exorcizing candidates for baptism. In the Golden Legend Peter was thrown into prison during the persecutions of Diocletian. There he drove out a demon that had possessed Paulina, the daughter of his jailer Archemius. That night he also appeared to Archemius in a vision, clad all in white and holding a cross in his hand. The jailer and his family then came to believe, and they were baptized by the priest Marcellinus.
When the prefect heard of all this he ordered that all the parties be executed. "The pagans" stabbed Archemius to death with a sword, stoned Paulina and her mother, and beheaded Peter and Marcellinus.
Images of St. Peter the Exorcist are rare. Usually they give the saint a promotion into the clergy. Jameson (II, 244) mentions two works in which he is dressed as a priest: a fragment from the Roman catacombs and a Renaissance painting where he and Marcellinus baptize Paulina together.
In the 12th-century mosaic at right, Peter is tonsured and dressed as a deacon in a procession with other deacon saints. The second and fourth deacons in the procession hold censers while the first and third (Peter and Lawrence) hold hand crosses. The crosses may be intended as attributes: Peter was holding a cross when he appeared to the jailer in the vision, and Lawrence is often represented with a ceremonial cross.
Caxton may have been influenced by this iconography when his translation of the Legend rendered the Latin title De Sancto Petro Exorcista as "The Life of S. Peter the Exorcist or Deacon."
Prepared in 2014 by Richard Stracke, Emeritus Professor of English, Augusta University