I love the looseness of watercolor. I took a watercolor class in my last semester of college, and it really was one of my favorite art classes. I had a hard time doing anything super loose like this, but I've learned to really appreciate watercolor, from Bill Watterson to John Sargent to Anders Zorn. It makes me want to find time to do watercolor again.
Anyway, this illustrator's name is Doug Slack, and he has the most adorable watercolors of muppets. Super Grover is probably my favorite, but you should really check out Kermit's Squinchy Face as well.