Final answer:
The Spanish explorer Juan Ponce de León landing on Florida and claiming it for Spain in 1513, became the first European to do so. However, he is most known for his search for the mythical 'Fountain of Youth'.
Step-by-step explanation:
The explorer referred to in this question is likely Juan Ponce de León, a Spanish explorer who conducted a significant expedition in Florida and the southeastern U.S. In 1513, he landed on the east coast of Florida and claimed it for Spain, reportedly becoming the first European to do so. However, his most significant finding was his search for the mythic 'Fountain of Youth', a body of water said to grant eternal youth to whoever bathes in it or drinks from it. Despite his extensive exploration, Ponce de León did not find this fountain, something that has fascinated historians and adventure seekers for centuries afterwards.
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