Master of the Winkler Epitaph
St. John at the Latin Gate
The man in the white beard appears to be the Emperor Domitian, who ordered that the saint be boiled in oil. The title given this image at its Wikimedia page is "Martyrdom of St. John the Evangelist," but it was not a martyrdom because St. John survived and was then exiled to the island of Patmos.
Read more about St. John the Evangelist.
Source: Wikimedia Commons