Who is Infantryman Jose Villasenor from The Killing Zone: My Life in the Vietnam War and what is their importance?

Jose Villasenor is one of the squad leaders in Lt. Downs' platoon. He is described as a swarthy, stocky Puerto Rican, who breaks into Spanish when excited. He participates in the battle in the jungle with Lt. Downs and Spaag, where Lt. Downs is slightly wounded, and many other battles. He is described as always looking for the funny side of situations.