As an overpowering culture of the world, the U.S. is often accused of culture creep. Throughout the world, one can find the influence of Hollywood on local media, U.S. pop culture loanwords intermixed with local language, and U.S. brands on local store shelves. So it is only right that kids in the United States absorb the culture of another country secondhand. Of course, I'm talking about Japan.
However, this culture has always seen a bit of a translation barrier as it came over. Not only is there the fact that some translations are hilariously bad due lack of skill of the translater, often the folks directing the translation worry that U.S. audiences will not understand or will have their sensibilities offended by a direct translation. This has resulted in such oddities as the alcohol often being turned into coffee or milk, editing of series to recast somebody else as the main character, and even the gender change of supervillains. It also somehow resulted in the changing of the hero in Mega Man.
That's right. In Japan, Mega Man is actually known as Rock Man (ロックマン). This is part of an overall musical theme to character names throughout the series. Rock Man's sister robot is named Roll, so they are Rock'n'Roll. The predecessor to Rock Man, Protoman, is known in Japan as Blues (ブルース). And so the sad end of Blues led to the creation of Rock and Roll.
There are multiple other musical references that were actually retained through the translation to English, which suddenly make a lot more sense once you know that background. The helpful bird-like robot Beat appears in multiple games. The boss Bass retains a musical name, but is known in Japan as Forte (フォルテ) instead. Accompanying him in this change is his dog-like robotic companion who went from the Gospel (ゴスペル) to Treble. And the adorable servbot Tron Bonne is a play on trombone.
Why, given the amount of effort that went into these plays on words, was the name 'Mega Man' used instead? It would seem an executive at Capcom, Joseph Morici, simply didn't like the name. What a kick in the pants.