Gustaf Aulén (1879-1977) was the Bishop of Strängnäs in the Church of Sweden and the author of Christus Victor: An Historical Study of the Three Main Types of the Idea of Atonement in 1931. This classic work analyzes the doctrine of the atonement of Jesus, suggesting that the three main interpretations in Christian history are the Christus Victor theory, the Satisfaction theory, and the Moral Influence theory. Aulén is also known in the Swedish Lutheran Church as a composer of widely used church music.
Gustaf Aulen interacts with major criticisms of the Reformation by Eastern Orthodox, Roman Catholic, and Anglican writers and sets the record straight about what the Reformation was trying to accomplish, and what it did accomplish, dealing with issues like tradition, justification, union with Christ, worship, and the succession of the Church. A really remarkable little book that took me far longer to finish than I intended. Still, nothing short of a great read. If you can find a copy, I do recommend picking it up.