The Composite Bowman is a very powerful ranged defensive soldier. You can get it by event rewards and ruby offers., He is ideal for defending ranged attackers. This soldier has to be healed with Rubies.
The Composite Bowman appears as a prize in a lot of events along with the Flame Bearer, often in the Wheel of Fortune as a level 1 prize. They can also be obtained in certain Mercenary Missions.