Who is Captain S. Payne Best from Bonhoeffer: Pastor, Martyr, Prophet, Spy and what is their importance?

This British officer, watchful and sardonic, was imprisoned with Bonhoeffer during his final two months of life at Buchenwald. Best survived the war, and his memoir of his experiences during his imprisonment is the primary source of information about Bonhoeffer's life in those last days, since none of Bonhoeffer's writings themselves survived.