Percival Lowell (1855 - 1916) was a Harvard educated businessman, writer, and astronomer. He is most well known for writing books speculating that the canals on Mars were built by intelligent life. Near the end of his life, one of his speculations turned out to be more long lasting. He searched for a 'Planet X' beyond the orbit of Neptune based on unaccounted for variations in the orbits of Neptune and Uranus. While it turned it that the orbital variations were due to a lack of understanding of the planets themselves, it did lead to a search among astronomers and Pluto was found in 1930.
Lowell is also credited with instigating the theory that intelligent life exists on Mars. During the early 1900s, while observing Mars from his observatory in Flagstaff, Arizona, Lowell noted that there were canal-like features on the Martian surface. He attributed these canals to intelligent life, a belief which caused him ridicule in the scientific community.