Who is Hamish McLeod from A Test of Wills and what is their importance?

Hamish McLeod is a dead man, killed in France during World War I, but he lives on in Ian Rutledge's head as his conscience and his coping mechanism. McLeod was a corporal under Rutledge's command who, under fire, refused to lead an attack on a machine gunner. With no other choice before him, and pressure from higher orders, Rutledge had McLeod arrested for failing to obey orders. Rutledge himself led the charge, taking the machine gun emplacement.