Giotto, Back of The Stefaneschi Triptych

Circa 1320
Tempera on wood
Pinacoteca Vaticana, Rome

In the center Saint Peter presides from his throne holding the keys that are his attribute. Two angels flank the throne, below them two saints, and below the saints two donors, one of whom is also a saint.

The saint on the left of the throne wears military garb and treads a small dragon with his right foot. Two military saints are associated with dragons: George and Theodore. George usually has a red-cross shield, so I would suggest that this is Theodore.

On the left panel are St. James the Greater (pilgrim's stick), St. Paul (book and some sort of baton). On the right, St. Andrew (long cross) and St. John the Evangelist (beardless with book and pen)

This image in full resolution
Back of the triptych, left panel: The Martyrdom of St. Peter
Back of the triptych, right panel: The Martyrdom of St. Paul

More of St. James
More of St. Paul
More of St. Andrew
More of St. Peter
More of St. Theodore
More of St. John the Evangelist

Photographed at the site by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.