http://www.movielabs.org/creativeworks/model#isPortrayalOf
Property 'is portrayal of'

ObjectProperty

Contribution and ((has contributor role value Actor) or (has contributor role value Dubbing actor) or (has contributor role value Stunt actor) or (has contributor role value Self) or (has contributor role value Voice actor))

is portrayal of

Character

is portrayed by

If this contribution is a portrayal by an actor of a character, this property identifies the character being portrayed.

By making the portrayal a relationship between a Character and a Contribution, we avoid the messy implications of having both a class Portrayal and a class Contribution. If you want to think of the portrayal as an instance (an object), it would be the instance of the class Contribution that is the subject of this property.