Clarance Walker is a Marine Colonel.
Colonel Walker was in charge of an Allied Forces attack on an Al-Qaeda base in Afghanistan, and arranged a mission for British SAS and Marine forces to plant a targeting laser within the mine to allow for a bomb drop.
Walker was not happy when Shane Schofield and Book II arrived talking of additional forces in the mine, as he was still waiting for the laser to be set up. However when a rougue Spetsnaz unit arrived and entered the mine, Walker was prepared to listen to Schofield, only to see he was going into the mine himself.
When the targeting laser was ready, Walker called in the bomber and set an order for evac crews to be ready to pick up any survivors from the mine entrance before the blast.