He had the money that Gatsby couldn't provide. When she meets with Gatsby after the war, and finds that he is very wealthy, she falls for him. Daisy is a very material person. She needs to have money. She was very much in love with Gatsby, but because he wasn't wealthy, she married someone who was.
Daisy focuses on the outward rather than the inward.
Tom Buchanan Tom is definitely the antagonist in the story. While Gatsby is at war, he uses his money to win Daisy over and marry, knowing very well of her relationship with Gatsby. He then precdes to have an affair with Myrtle, George's wife and makes no effort to hide it from Daisy. He treat Myrtle even worse then he treats Daisy. Even though he is having an affair, he stands in the way between Gatsby and Daisy.