To AprilSeven: First the public did not plead with Tezuka to make Astro Boy younger. It was just that the younger he made Astro Boy appear the more his popularity seemed to grow.
It should be obvious to you that the first series was the most popular by the number of episodes that were made. To this day I think that only Dragon Ball Z, Sailor Moon and Gatchaman have as many episodes as the original TetsuWan Atom.
Astro Boy did well until its final season, 1966 coinciding with the publication of the episode known as "The Blue Knight". As I remember reading, at the suggestion of one of his editors, Tezuka wrote a story where Atom goes against humanity. That episode was "The Tale of the Blue Knight".
After this tale was published Astro Boy's popularity declined. Of course there are other factors, but that story is thought of as being a main contributor to Astro Boy's decline in popularity.
To Novacain: I want to clarify, that because the 1980s series did not do as well as expected it was considered a failure; not that it did poorly.
I believe the 2003 series did well judging by the number for ratings I read in Newtype magazine in English. The series was intended as a way to spark interest in the Atom character for its 40th anniversary.
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