The horse's name is Sterling. Sterling began as a "doodle" I drew one day. Then the cliffs and the tree were drawn. As I looked at the drawing, I wondered why this horse was rearing up at the edge of a cliff, gazing intently at a gnarled tree on the opposite side of the chasm.
This drawing told a story of it's own, and just had to be included in Winky & Wonder. You can discover what that story is in the very last chapter of Book II.