St. Dominic Worshipping the Trinity
Baptismal Chapel, Cáceres Cathedral, Cáceres, Spain
By the 18th century it had become standard to represent the Trinity with the Son on the Father's right and the Holy Spirit hovering between them. In this case the Son's right hand is broken off and may have once held a cross, which has been a common feature in this type of Trinity image.
The audio guide provided by the cathedral identifies the saint as Dominic, but there are no attributes other than his Dominican habit. Placing Dominic before the Trinity specifically may reflect his preaching against Albigensianism, which holds that the Son and Holy Spirit are mere creatures of the Father (Catholic Encyclopedia, s.v. "Albigenses").
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Read more about St. Dominic.
Read more about the Trinity.
Photographed at the cathedral by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.