Like anatomy? That's a start, but character comes from a deeper place than mathematical precision. The real story comes from expression. Whether it's body language or facial expressions, people are constantly communicating. If you neglect this aspect of personality when learning to draw people and characters, you might end up with 'lifeless' or 'plastic' results. This video introduces some good examples for study including my favorite: Glen Keane. Glen does not seem to have a personal website I can promote, though a quick google search will lead you to fan-collected images.