Yes, I've never heard much about it either.
In all my interactions with Christianity no mention was ever made.
Supposedly he was from Briton.
Pelagius was a monk, from Britain or Ireland, who was in Rome in the time of Pope Anastasius (399-401 CE) and took exception to what Augustine of Hippo wrote in his
Confessions in relation to "the gift of continence": (Lord),
grant what you command, and command what you will (Da quod iubes et iube quod uis, x. 40). No, said Pelagius loudly, if you're not responsible for the morality of your deeds, that means you're not answerable when you sin.
In the resulting brawl, Augustine and Jerome attack his ideas, Pope Innocent excommunicates him 417 CE, and he disappears from history, though said to have died in Palestine. However some of his followers were still around, and were charged with asserting that
─ Adam would have died whether or not he'd 'sinned'
─ Adam's 'sin' injured only Adam, not the human race
─ children are born innocent
─ no one dies because Adam 'sinned', and no one will rise again because of Jesus' resurrection
─ each of the law and the gospels offer a way to heaven, and
─ there were humans without sin before Jesus' time,
all of which notions were pronounced heretical.
As a result, the writings of Pelagius are thin on the ground, though not entirely absent.
It's plain as day that Pelagius was right, but since when has that mattered in church politics?