what does "a shadow of what he had been" mean

The phrase "a shadow of what he had been" suggests that a person has significantly declined in some way compared to how they used to be. This could refer to a deterioration in physical health, mental well-being, skills, personality, or overall vitality. Essentially, it implies that the person is far less vibrant, capable, or influential than they once were, much like a shadow is a mere outline or a lesser representation of something more substantial.