Who is Lieutenant Death from The Surrender Tree: Poems of Cuba's Struggle for Freedom and what is their importance?

Lieutenant Death learned the slave catching trade from his father, while he was just a boy. He spends most of his time searching for Rosa and determined to end the rebellion by killing her.

According to history, there was actually a slavehunter known as Lieutenant Death. There is not, however, any evidence that he assisted the Spanish military or pursued Rosa.