Edward has a bunch of titles in Henry VI, Part 3. First he's Earl of March; then he's Duke of York; and then he's King Edward IV. All you need to know about this guy is that he's York's oldest son, and that he takes on his dad's battle against Henry for the crown. Easy enough, right?
Once his dad dies, Edward goes after the crown, which is now, in theory, his. He puts up a good fight, and at first he has a lot of supporters, but he quickly tunes out his brothers and supporters. Who needs them? He gets drunk on power and decides he'll make the decisions about what's best for England. (He's a cheap drunk, by the way; one swig of power, and he's wasted.) For example: even though he's sent Warwick off to France to get him a wife, Edward up and marries Lady Grey. Why?
That's a tough one to answer. Lady Grey doesn't have money or political power, and Edward's brothers think the whole thing is a very bad idea. But Edward is already a smitten kitten: Lady Grey flat-out refuses his request that she become his mistress, so he proposes marriage instead.
That's a pretty extreme move just to get into someone's pants. It comes out of left field and has a rippling effect: Warwick ditches Edward; George forms his own army; and Richard tells us he plans to take the crown. Hmm. We wonder what's so amazing about Lady Grey to create such drama. Or is it just that Edward is a spoiled kid who's not all that into making mature, king-like decisions?
In the end, Edward and his posse are successful. He becomes king, and he delivers a speech about how England will have nothing but peace from now on, "with stately triumphs, mirthful comic shows" (5.7.44). Translation: "I got want I want, so from now in, it's gonna be one giant par-tay."
That's wishful thinking for you. Edward turns out to be pretty naive when it comes to the crown and strategies for keeping it. Just because he has it, he thinks everyone will stop clamoring over it, when that's all they've done for the last 30 years. Right.
Edward's also way too trusting when it comes to his brothers. George forms an army against him, and Richard plots his demise, but Edward thinks they're just one, big, happy family. Henry VI, Part 3 may end on a happy note, but something wicked this way comes. Richard makes sure of it.