Who was the explorer who found foutain of youth?

No-one, for the simple reason that it did not exist. There are however stories that Spanish explorer Ponce de Leon went out searching for the fountain. Those stories however only emerged after his death. Nowhere in Ponce de Leon's own correspondence is there any mention of the hoped-for existence of such a fountain, nor of any effort to find it. Also, none of his documented expeditions included the search for it. So the whole story, including Ponce de Leon's involvement in it, can be considered a myth.