The Sandworms of Arrakis. These guys were fun to conceptualize, as I didn't want to be a slave to Lynch's film versions, which while they were the best part of the film (they looked great) but they were in turn, really based off of John Schoenherr's paintings. While Schoenherr's work is awesome, I just wanted to do something a bit different, and ended up looking to Pelican Eels for inspiration.
That caps off the series. I'm aware that there are even more characters, but I wanted to tackle who I considered the most important.