[math-fun] Kaplansky's Obituary

I don't think I saw any mention of it here, but Kaplansky passed away little over one month ago, on June 25. Here's a link to a nice obituary . . . but I wasn't able to extract specific results of his from this: < http://www.signonsandiego.com/uniontrib/20060714/news_1m14kaplansk.html> Actually, I'm curious -- if any cognoscenti would care to explain some theorems he's famous for, I'd be very interested. --Dan