Shakespeare’s Polonius is definitely a much more forward looking Renaissance man than that which is portrayed by Castiglione. The latter describes the ideal man as a lackey of the establishment, a courtier who does his utmost to curry favour from the rich nobleman to be able to advance his own lot. This perhaps is the expectation of the day but in Shakespeare’s Polonius all that seems to change.
Polonius advises his son to listen to everyone but to please no one. In a sense he is going much deeper than Castiglione whose only scope seems to be to impress those above him so that he will manage to advance himself in life. With Polonius all this seems to change as the main thrust of the argument is that the man who has a mind of his own and is able to think will advance substantially more in life.
What may initially be a small change is quite a large one as Shakespeare is subtly advising his son not to embrace the trappings of power and fame but to act with intelligence and his own mind. It is a world apart from the portrayal of Castiglione who wants his man to be witty, carefree and attractive, superficiality seems to be the order of the day in this description.
Messina’s painting shows a sober and serious personage who is not much preoccupied on looks and appearance but rather seems to be wily and sharp in his overt bearing. It is the typical man which Shakespeare must have had in mind for his own version of the Renaissance man.