Some additional facts on Carl Barks:
Since Disney and pretty much all "funny animal comics" never listed credits for the people who worked on them, fans learned to recognize artists and writers through their styles and storywriting. Barks, whether it was an adventure-themed story or a short comedy piece, became instantly recognizable and was known to many fans as "the good artist" or "the good duck artist."
One of the ways he was able to create such a rich tapestry to his adventure stories was that he used as "reference" issues of National Geographic and the Encyclopædia Britannica.
In his career, he is said to have drawn 6215 pages, 190 covers, and written 396 scripts for the comics.
When he retired from the comics in 1966, he took to oil painting. Between 1971 and 1976, he painted some 122 Duck-themed works. At that time, Disney decided to step in and restrain him from further use of their characters (the paintings were becoming highly valuable). He continued painting, though, using his own subjects (creating and painting were the things that motivated him and made life enjoyable).
In later years, he was able to return to the Ducks he loved and helped create by working through the Disney licensee Another Rainbow, where his oil paintings were turned into lithographs and collectibles. He continued painting up until his death by leukemia in 2000 at the age of 99.
(Some info from www.fmi.uni-passau.de/~zimmerth/comics/barks/index.engl.shtml)