John Bauer was a Swedish illustrator, born in 1882, who primarily painted fairytale creatures. His work has been influential in subsequent fantasy illustrator's works.
What stands out to me is the obvious inspiration Bauer's work was to muppet-men, Jim Henson and Frank Oz. Particularly their film "The Dark Crystal" owes much by way of creature design as well as overall tone to Bauer's illustrations. It also seems apparent that this influence made it's way down to "Fraggle Rock" (clap clap).