Clyde Tombaugh
In 1930, Clyde Tombaugh, working at the Lowell Observatory, discovered Pluto near the location expected for Planet X. Partly in recognition of Lowell's efforts, a stylized P-L monogram (♇) – the first two letters of the new planet's name and also Lowell's initials – was chosen as Pluto's astronomical symbol. However, it would subsequently emerge that the Planet X theory was mistaken.