(1) Joseph Butler (1692-1752), the Bishop of Durham claimed that happiness was a by-product. That is to say, when your desires for things other than happiness itself were satisfied, then you experienced happiness. According to Butler, one could not directly pursue happiness itself. Rather one pursued other goals in life and as these were achieved, happiness could result.
Butler also seems to have thought that the pursuit of happiness underlay everything in some sense. He said “when we sit down in a cool hour, we can neither justify to ourselves this or any other pursuit, till we are convinced that it will be for our happiness, or at least not contrary to it”
~ Notes from The History of Western Ethics, by Britannica Educational Publishing, Ed. Brian Duignan
(2) Prodicus of Cos (465 bc – 395 bc), a Sophist philosopher, was the first to explicitly state that happiness is our overall goal in life.
~ Similar to Butler.
(3) John Stuart Mill (1806-1873): basically equated happiness with pleasure.
Notes from Ancient Philosophy: A Very Short Introduction, by Julia Annas, Oxford University Press