The actor's physical type is the main consideration. It isn't and shouldn't be. Does the actor "look the part"? It is the simplest question to deal with. The director deludes himself who yields to the temptation to believe that an affirmative answer settles the matter. An actor's looks will impress an audience initially but after his first five minutes on stage it becomes aware of what he or she communicates (or fails to communicate) through acting!