This is my 17th restoration of 16th Century windows. This window became quite a history lesson. The below information is about the person in the portrait.
Artist Lucas Cranach (1472-1553) became the court painter to the Saxons in 1505. In 1537 he painted a portrait of Duke Henry of Saxony on lime wood. Someone, perhaps Cranach himself or his son, used that lime wood painting as the model for a portrait on glass.
The original wood painting was lost, stolen or destroyed during WW II. It was in a museum in Dresden, a city the allies firebombed. The glass portrait, however, survived. It was already in the United States.