Azure Blue (also known as Blue Glaucus in some translations) is the alleged direct descendant of Olaf the Blue, a navigtore Viking, considered the first European to discover North America.
The villain appears in the history of Donald and the crest Viking, built in 1951 by Carl Barks. In this adventure Azure tries to prove his descent from King Olaf to be able to proclaim the entire American continent. To do this it must regain possession holding an old Viking crest, that would be the ultimate proof to establish that America was discovered by his grandfather and then he would be the rightful owner.
Since the '90s Azure Blue was able to count on other appearances: in particular, has been taken over by Don Rosa in The Lost Charts of Columbus and also appears in an Italian story, Mickey and the Emperor of America Massimo de Vita (both these works were conceived as developments in the case of Donald and the crest Viking, and in both it takes up the theme of the mad ambition of the character to rule on the entire continent).