Who is Death from Collected Poems and what is their importance?

Death takes Owen above the battlefield where he can watch the carnage with a bird's eye view. The sight terrifies Owen, who then falls back to the ground with Death by his side. Afterward, Death tranforms into a worm, showing Owen his own severed head. It is at this point that Owen sees Death not as his enemy..... but rather his friend and companion, a friend who stays with him throughout the war.