In reality, the character of Stanley basically goes from bad, to worse, to worst. His development in the play resembles that of a storm: the atmosphere changes at first, then the wind begins to blow and, finally, destruction ensues.
This is how his development resembles the changing atmosphere of an incoming storm. We find him nowhere amicable nor receptive in Act I. There he demonstrates that he is a chauvinist who treats his wife as property. The allusion to this comes when Stanley, nonchalantly, throws a slab of meat at Stella expecting her to catch it and, of course, feed him with it.
Not long after that, we see that he has very little sympathy for Blanche as she arrives to the apartment, even when she tries quite hard to charm him with her demeanor and behavior.
As the play progresses, so does Stanley's violence. We hear about the beating he gives Stella even though she is pregnant. Then he begs for her screaming and crying like a co-dependent. All of his behaviors denote that he is overall unstable: he just has not come out all the way.
Stanley begins to take an overall dislike against Blanche when he finds out about her affinity with Mitch. Then, he takes it upon himself to do a search and find Blanche out. Here we find his anger growing, although not yet blinding him entirely. However there is more to come.
When Stanley's wrath comes to an all-time high, he confronts Blanche, and then debases her by raping her and leaving her to the end of her wits. He literally assassinated her character and her integrity. Also, he killed the last shot at a dream left in Blanche's life. This is the epitome of a destructive force of nature, and Stanley represents that innate, evil ire that lives within those with a dark soul. His ultimate step toward the development of the character is an ultimate act of disproportionate evilness and sadism.