Despite maturing into a noble, self-sacrificing hero, James Potter started out – in the words of his own future wife – as an ‘arrogant toerag’ at school.

Aside from countless detentions for bad behaviour in class, young James would merrily inflict his considerable talent for hexing directly on fellow students. Sometimes at random in the corridor, or on one occasion by making the hapless Bertram Aubrey’s head swell to twice its usual size.

The meanest example of James Potter’s ruthless ways was of course against Severus Snape. Following an O.W.L. exam, James, with partner in crime Sirius Black, confronted the vulnerable young Snape, pinned him to the ground, filled his mouth with pink soap bubbles then lifted him into the air, threatening to completely undress the pale, slight Slytherin boy in front of a giggling crowd of fellow students.

Lily Evans was the only pupil who stood up to this crowing, self-regarding ruffian. In spite of this – or, more likely, because of it – James soon became infatuated with the beguiling red-haired, Muggle-born witch.

Which was all the more intolerable for Snape. How could he, an oily-haired, pallid wraith, who’d fancied Lily since boyhood, compare with this handsome, cocksure Quidditch-playing newcomer?

In truth, he couldn’t, and Snape bore such a bitter grudge against him that he even went on to resent James’s son Harry. And who could blame him, when young Harry bore such a resemblance to Snape’s tormentor, while at the same time having the same limpid, lovely eyes of his mother Lily?

So it begs the question – why was James Potter such an awful rotter? Should not those who are blessed with talent, looks and a large group of friends be all the more munificent to those less fortunate?

Sadly this is seldom the case. Perhaps one reason – not an excuse, but a reason – is James’s upbringing. Euphemia and Fleamont Potter tried and failed for many years to bring a child into the world before baby James came along. They were much older, and wealthy, so James grew up in a doting environment without the compromise of siblings, in a home without material limits.

Certainly, that’s not inherently a negative thing. Far from it – love, comfort and plenty should be the hallmark of every child’s upbringing. But, arguably, sometimes a child is more inclined to empathy if they grow up with boundaries, and an instilled sense of humility. Hence, perhaps, why James appeared to have ‘that indefinable air of having been well cared for, even adored’ which Snape so conspicuously lacked, and why he behaved in such a manner sometimes. This was only enhanced by his fortunate association with handsome, cool Sirius and thoughtful, intelligent Remus Lupin.

Snape, to be fair, deserved some share of blame for his woes. He and James locked horns from the first time they met on the Hogwarts Express. Snape also rounded on James’s spirited wish for a place at the Gryffindor table with the acid-tongued ‘If you’d rather be brawny than brainy.’

The worst of it was that, when eventually released by Potter following the O.W.L.s incident, an enraged, humiliated Snape insisted he didn’t need the help of Lily, a ‘filthy little Mudblood’. Which didn’t go down too well with his beloved, and sure enough she eventually swanned off with the bad boy Potter.

But let’s not be too harsh. Young James Potter also did many fine things. When it emerged his close friend Remus Lupin was a werewolf, far from shunning him, he took the extraordinary step of learning to become an Animagus himself. In his later student career he stopped hexing random students in corridors, and indeed went on to become Head Boy. Even his naughty antics came good in the end – the Marauders’ Map, co-created with his closest pals, became invaluable to the next generation of Hogwarts students in their fight against evil.

Nobody is ever perfect. James Potter’s own wife, again, initially claimed she’d rather go out with the giant squid. But, as his best friend Sirius Black later remarked: ‘A lot of people are idiots at the age of fifteen. He grew out of it.’

Each month Pottermore will try to defend the more… questionable characters from the Harry Potter stories. Come back next time when we make the case for Kreacher.