Hans Hörbiger (1860-1931) started his career well, as an engineer in 19th-century Austria who was primarily connected with the Budapest subway system, inventing a range of valves, compressors and general "improvements" for the subway project. He is most well known for his pseudoscientific "World Ice" theory.
Welteislehre ("world ice theory") goes roughly as follows: outer space is filled with some kind of viscuous medium; drag from this medium is causing the Moon to spiral inwards towards Earth (which is itself spiralling towards the Sun); and the current moon is but one of many moons, the previous ones having crashed into earth long ago, causing such disasters as the Great Flood. The theory also holds that all the heavenly bodies except Earth and the Sun are covered with thick layers of ice. The Milky Way is nothing but an enormous mass of lumps of ice, continually spiraling into the Sun, which is how sunspots are formed.
Hörbiger did not come to this theory by research; apparently it came to him in a "vision."
This entertaining theory became popular in certain circles - the Swedish botanist Nils Heribert Nilsson was an advocate, as were the Nazis, who would believe almost anything if a German came up with it (especially if the prevailing theory that it is challenging was developed by a Jew).