It’s easy to discount and ridicule Gloucester’s bastard son, Edmund from the moment the play begins. Only the bastard, destined to live in the shadows of his legitimate siblings. In this historical setting, illegitimate children were meant to be whisked away, to rot in a cellar to become a priest, anything to stay out of the legitimate children’s way.
This was not a lifestyle meant for Edmund, and it is perfectly reasonable for him to try and escape his bastard label, which would hold him back from what he wants to do in life. In time based heavily in titles, legacy and respect he has to find some way of moving up the social later. While being considered he is prevented from acquiring land and titles, things vital for success, so a natural course of action is to remove his direct competition in Edgar. While his actions actions and their consequences are less than noble, it is at least admirable to some extent his ability to pray on people’s (Gloucester and Regan) insecurities like no other.
He is quite politically savvy, moving his way between Gloucester, Regan and Cornwall. He can quickly identify what each person fears and uses it to advance his own agenda without them noticing his motives. He does also achieve what he wanted, to be recognized as part of normal society, however only after he betrays his father. After Gloucester’s blinding it makes it a lot harder to defend him but we’ll see what happens in act 5, maybe he will redeem himself.