Drago seemed like a poor match for Dany at first, but they were perfectly suited and between them grew a great love. He seemed unstoppable, but was cut down by a flesh wound. Returned by Blood Magic as a changed being, Daenerys took her husband's life again so he wouldn't suffer.
Tyrion: Let me give you some advice bastard. Never forget what you are. The rest of the world will not. Wear it like armor, and it can never be used to hurt you. Jon: What the hell do you know about being a bastard? Tyrion: All dwarfs are bastards in their father's eyes.