The Doctor, who comes from Bologna or around that area, is not only a character of the Commedia dell'Arte, but also a mask which gives the possibility of teasing the "powerfully learned".
And we are talking about a Doctor, half charlatan (and more than that in those times!), but especially somebody who has studied, and uses his "superior knowledge" to magnify his person.
Dotor Gracian is the most ancient impersonation of the Doctor,
and in 
another version of this same image, there is some text added, that goes like this:
"Mi son quel biel Duttor da Francolin
Ch'à studiat, Bartol, Baldo, èl'Boccalin."
"I am that handsome Doctor from Francolin
Who have studied Bartol, Baldo and Boccalin. *"
* He shows here how knowledgeable he is:
-Duttor da Francolin: character sometimes used in the comedies of the XVII century, may very well be one of the characters in the satyrical play “La Pirlonea” (The Stupid Thing)
-Bartol, or Bartolo: possibly another comedian
-Baldo: very likely Baldo Rotari (comic actor)
-Boccalin: Traiano Boccalini (Italian satyrist writer)
Of course for the "average public", he definitely is a much learned guy ... right.
