Who was Gambrinus?

So the beer trivia post got me looking a little more into the Patron Saint of Beer, Gambrinus, a saint even those of us who are non-Catholic can pray to (and probably have after having a few too many). I lifted this from Wikipedia:

Gambrinus is a legendary king of Flanders, and an unofficial patron saint of beer or beer brewing.

The origin of the character is most widely believed to be John, Duke of Burgundy (1371–1419), who some also believe to be the inventor of hopped malt beer. One of Charlemagne's cupbearers was also called Gambrinus.

In what is possibly the earliest known record of the name, the German poet Burkart Waldis mentioned Gambrinus in the year 1543, explaining that Gambrinus learned the art of brewing from Isis, the ancient Egyptian goddess of motherhood and fertility.

Possible Latin etymologies of the name include cambarus (cellarer) and ganeae birrinus (one who drinks in a tavern). The Gambrinus brewery of Plzeň, Czech Republic explains the name as originating from Jan Primus (John the First), referring to John I, Duke of Brabant.[1]

Although not as likely, Gambrinus might also derive from camba, a word from the Celtic language family that refers to a brewer's pan. Alternatively, Gambrinus may be a corruption of the name Gambrivius.

Gambrinus is often depicted either in kingly garb, dressed as an English knight of the Middle Ages, or (less commonly) as a plump old man.

Because of Gambrinus' significance, numerous European and North American brewers have adopted the character (or his name) in their beer brands. Several notable breweries are named for Gambrinus, including:

Gambrinus Brewery of Plzeň, Czech Republic
Gambrinus of Mulhouse, Alsace, France
The Gambrinus Company of San Antonio, Texas, U.S.A.
Gambrinus Brewing Co. of Oshkosh, Wisconsin
The Gambrinus Brewing Company of Columbus, Ohio, U.S.A.