Who is Lieutenant "Shadow" from With the Old Breed, at Peleliu and Okinawa and what is their importance?

Lieutenant Shadow, an officer, is tall, skinny, and incredibly sloppy. The men hold his sloppy appearance in disdain. Sledge offers his nickname only, probably because he has nothing positive to say about the man. Shadow is moody, ill-tempered, excitable, and obnoxious. Most of the men immediately dislike him. On one occasion, Shadow reprimands John Redifer, a buddy of Sledge's, for demonstrating bravery under fire. He apparently joins K/3/5 during the early phases of operations on Okinawa and first appears in Chapter 11. After Lieutenant Stanley is evacuated due to malaria, Shadow assumes command of K/3/5, much to the dismay of Sledge and others. Although he is disliked and is often verbally abusive, Shadow appears to be at least a competent officer.