Old time prophets can be really fun to draw, I think this is mostly due to the beard. Some people will tell you that you can have just as much fun drawing a wizard or Rip-Van Winkle but it's just not true. Bearded wizards are fun up until the point where you have to add the goofy hat and wand, then they just seem silly. Moses is probably the most fun he's well over 100 years old and he's been wandering around in the wilderness for forty years.
Like my last post his came from something in my sketchbook (probably something I did during church). In the original sketch Moses was just looking up at a blank space so I added the staff and the snake to give him something to look at.