The doctrine of original sin was/is largely the work of saint Augustine in his reflections on a passage from Romans. The passage follows
Romans 5:12 Therefore, sin entered the world through one man; and through sin, death; and later on, death spread to all humankind, because all sinned. 13 As long as there was no law, they could not speak of disobedience, but sin was already in the world. 14 This is why, from Adam to Moses, death reigned among them, although their sin was not disobedience, as in Adam’s case—this was not the true Adam, but foretold the other, who was to come. 15 Such has been the fall, but God’s gift goes far beyond. All died, because of the fault of one man, but how much more does the grace of God spread, when the gift he granted, reaches all, from this unique man, Jesus Christ. 16 Again, there is no comparison between the gift, and the offense of one man. The disobedience that brought condemnation was of one sinner, whereas the grace of God brings forgiveness to a world of sinners. 17 If death reigned through the disobedience of one and only one person, how much more, will there be a reign of life, for those who receive the grace, and the gift of true righteousness, through the one person, Jesus Christ. 18 Just as one transgression brought sentence of death to all, so, too, one man's good act has brought justification and light to all; 19 and, as the disobedience of only one, made all sinners, so the obedience of one person, allowed all to be made just and holy. 20 The law itself, introduced later on, caused sin to increase; but where sin increased, grace abounded all the more, 21 and, as sin caused death to reign, so grace will reign, in its own time, and, after making us just, and friends of God, will bring us to eternal life, through Jesus Christ, our Lord.