Our Lord Paid The Debt For Our Sins, But Who Or What Was That Debt Paid To?

As Christians, we hold that Jesus Christ died on the Cross to redeem humanity from the bonds of sin, and in doing so, paid the debt for our sins. 

The concept of a debt being paid implies a creditor, but who - or what - was this debt paid to? 

Within the Catholic tradition, this question has given rise to a profound theological discussion, one that touches on the nature of God, justice, mercy, and our understanding of salvation.