Flash forward to Aristotle's day, 335-ish B.C. Philosophers of the time considered happiness to be synonymous with virtue. In other words, do good to feel good. If you didn't feel good, it meant you weren't being virtuous enough. Now, we don't want to come off as cynical here, but it almost sounds like this was when they started using this elusive idea of happiness as a motivational tool. Happiness is the carrot on the stick that makes you do all of the things that keep society running smoothly.
"All of this will be worth it, once I'm able afford that crack habit I've been longing for."
After that, you get into medieval times when early Christians saw happiness as something a soul was to be rewarded with in heaven, and not something attainable in the mortal world. Then the Renaissance came along and brought us the concept of pleasure equaling happiness. Keep in mind, those two ideas weren't always connected -- the old-school thinkers described happiness as the overall state of somebody who had lived their life well, completely separating it from that feeling you get when you eat a warm cookie or play with a puppy.
"I'm deeply, spiritually satisfied about the number of puppies I've played with."