Why did Martin Luther change his surname from ‘Luder’ to ‘Luther' very early in his career? I was surprised to find out ‘Luther’ is not Martin Luther’s original surname but ‘Luder’ is. The Greek word έλεύθερος that was the origin of his Latin name was Eleutherius. You can see ‘uder’ does not quite sound as good as ‘uther’. You can hear the sound of the Greek word here: click on the speaker sign to listen

I have read that in the fall of 1517 he changed his name. So what would make Luther get so fussy about his name so that he wanted it to match the original Greek more audibly?
According to a book by James Nestingen,


  On Luther's "Gospel discovery," his "tower experience," I agree with Nestingen (and Lohse) that it probably coincided with his name change from Luder the Luther, "a small change based on the Greek word for freedom, elutherius. I see the similarity as too exceptional simply to explain Luther's name change as merely a respelling from Low/Middle German to High German.


http://www.amazon.com/Martin-Luther-James-A-Nestingen/dp/0800697146

The reason for choosing a word related to "freedom" has to do with the freedom offered by the Gospel.