Augustine of Hippo (354-430)
After his conversion to Christianity and baptism in AD 387, Augustine developed his own approach to philosophy and theology,
http://en.wikipedia.org/wiki/Augustine_of_Hippo
Pelagianism derives its name from Pelagius who lived in the 5th century A.D. and was a teacher in Rome, though he was British by birth. It is a heresy dealing with the nature of man.
Thus it denies original sin, the doctrine that we have inherited a sinful nature from Adam.
Pelagius has been condemned by many councils throughout church history including the following:
Councils of Carthage (412, 416 and 418)
Council of Ephesus (431)
The Council of Orange (529)
Pelagianism fails to understand man's nature and weakness. We are by nature sinners (Eph. 2:3; Psalm 51:5). We all have sinned because sin entered the world through Adam: "Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all men, because all sinned" (Rom. 5:12, NIV).
http://carm.org/pelagianism