Gustaf Aulén was a Swedish theologian best known for his work on the doctrine of atonement, particularly in his influential book 'Christus Victor.' Aulén proposed that the primary understanding of atonement should focus on the victory of Christ over sin, death, and the devil, rather than solely on the ideas of substitutionary atonement or moral influence. His work has significantly shaped contemporary discussions about atonement theories and their implications for salvation.