Who is the man in the Diamond Jack of the playing cards?

Answer 1

Hector of Troy
alternately, Roland of France

per the graph at the web below (this took me 1/2 hour to find your answer!)
Playing Card Historical Personage

King of Hearts Charlemagne

Queen of Hearts Judith (of the Book of Judith,
an Apocryphal Book of the Bible)

Jack of Hearts "La Hire," a famous French warrior
a.k.a. Etienne de Vignoles

King of Spades King David

Queen of Spades Pallas, a.k.a. Minerva

Jack of Spades Hogier the Dane,
one of Charlemagne's paladins

King of Diamonds Julius Caesar

Queen of Diamonds Rachel (of the Bible)

Jack of Diamonds Hector of Troy
alternately, Roland of France

King of Clubs Alexander the Great

Queen of Clubs Argine
An anagram of Regina

Jack of Clubs Lancelot