Percival Lowell (/ˈloʊəl/; March 13, 1855 – November 12, 1916) was an American businessman, author, mathematician, and astronomer who fueled speculation that there were canals on Mars, and furthered theories of a ninth planet within the Solar System.

He founded the Lowell Observatory in Flagstaff, Arizona, and formed the beginning of the effort that led to the discovery of Pluto 14 years after his death.

His texts are filled with observations and academic discussions of various aspects of Japanese life, including language, religious practices, economics, travel in Japan, and the development of personality.

The most popular of Lowell's books on the Orient, The Soul of the Far East (1888), contains an early synthesis of some of his ideas that, in essence, postulated that human progress is a function of the qualities of individuality and imagination.

"[8] At his death he left with his assistant Wrexie Leonard an unpublished manuscript of a book entitled Peaks and Plateaux in the Effect on Tree Life.

The Boston geologist George Russel Agassiz noted that Lowell made the decision to begin his observations after hearing that Schiaparelli began to experience failing eyesight.

[11] Beginning in the winter of 1893–94, using his wealth and influence, Lowell dedicated himself to the study of astronomy, founding the observatory which bears his name.

This marked the first time an observatory had been deliberately located in a remote, elevated place for optimal seeing which included enhanced image quality, sharpness and steadiness.

[14] In 1904, Lowell received the Prix Jules Janssen, the highest award of the Société astronomique de France, the French astronomical society.

With these writings, Lowell more than anyone else popularized the long-held belief that these markings showed that Mars sustained intelligent life forms.

He theorized that an advanced but desperate culture had built the canals to tap Mars' polar ice caps, the last source of water on an inexorably drying planet.

He began observing Venus in detail in mid-1896 soon after the 61-centimetre (24-inch) Alvan Clark & Sons refracting telescope was installed at his new Flagstaff, Arizona observatory.

A team of human computers, led by Elizabeth Williams were employed to calculate predicted regions for the proposed planet.

In addition, the discrepancies between the predicted and observed positions of Uranus and Neptune were found not to be caused by the gravity of an unknown planet.

[32] Although Lowell's theories of the Martian canals, of surface features on Venus, and of Planet X are now discredited, his practice of building observatories at the position where they would best function has been adopted as a principle.

[34] While eventually disproved, Lowell's vision of the Martian canals as an artifact of an ancient civilization making a desperate last effort to survive, significantly influenced the development of science fiction – starting with H. G. Wells's influential 1898 novel The War of the Worlds, which made the further logical inference that creatures from a dying planet might seek to invade Earth.

The canals, and even Lowell's mausoleum, heavily influence The Gods of Mars (1918) by Edgar Rice Burroughs as well as all other books in the Barsoom series.