In 1975, Toei released the first entry in a series of 10 movies called Truck Guys that featured as the protagonist a costumed trucker who drove his garishly decorated truck all over Japan. This movie was a big hit with both old and young, and caused a wave of Dekotora popularity to sweep the country. While Dekotoras were present throughout the 1970s, before the movie they were restricted to the north-eastern fishing transport trucks. It is possible that the movie was an attempt to popularize these kinds of trucks. In those days, ready-made parts for trucks were not easily available, so these trucks freely utilized parts from sightseeing buses or US military vehicles.
Since the late 1990s, Dekotora have been heavily influenced by the art of Gundam (a popular animated cartoon / movies series). In addition to the Gundam-influenced designs, it is common to see decorations that are more akin to modern art, or even retro designs that closely resemble those found in the movie Trucker.
From: http://en.wikipedia.org/wiki/Dekotora
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