We know about his love life, his childhood and his vices - he smokes but doesn't drink.
So it's surprising when you stumble upon a piece of information about the former child star that you hadn't already heard - like the fact that, aged 17, he tried his hand at poetry.
A quartet of his works, which tackled topics such as infidelity, prostitutes and Pop Idol, appeared in Rubbish magazine in 2007 under the pseudonym Jacob Gershon.
"I mean why would you bother with divorce?/It's somuch easier to slip away/And put a week aside so you can play," reads one particularly anti-Potter poem.
And six years later, the verse-loving star finds himself playing one of the most famous poets of all time, Beat Generation writer Allen Ginsberg, in Kill Your Darlings.
So what would Ginsberg have thought of Radcliffe's rhymes?
"He would have hated them," says the actor, laughing.
"Well, he probably would have said, 'Well done for being a 17-year-old writing poetry'. But he wouldn't have liked it, because it's far too rhyming and conformist."
That's not the only pastime of Radcliffe's the late poet would have struggled to appreciate.
The 24-year-old admits that while filming, he and co-star Dane DeHaan spent their spare time playing Fantasy Football.
"I'm not sure if Ginsberg would have been in our league if he was alive today," he says. "But we'd have invited him for sure."
It wasn't all fun and games, of course. Playing such a prominent character's no easy task - Ginsberg was a leading figure of the counter-culture, opposing materialism and writing explicitly about homosexuality at a time when it was still illegal.
As someone who speaks out about homophobia and supports The Trevor Project, which focuses on suicide prevention for young homosexual people, Radcliffe was well-suited for the part.
He said: "I hate any kind of prejudice or injustice, we all do, so if I can be a small voice to speak against it then that's fantastic."
Radcliffe has homosexual scenes, including a kiss with DeHaan and an explicit sex scene. While he seems relaxed about the doing the scenes, watching them back did give him an attack of body anxiety - though he's good humoured about it.
"I remember thinking, 'I'm in good nick'. And then I saw the scene and thought, 'I look like a whippet'. But I guess it would have been inappropriate for Ginsberg to look like he'd been going to the gym."
It was an incentive to beef up, he admits, not that he'll be showing off the results of his efforts soon - while recently filming a second series of A Young Doctor's Notebook, Radcliffe told producers he wanted to avoid getting naked, though he will strip off in films Horns and The F-Word, out next year.
Radcliffe's body has been a talking point since he starred, frequently starkers, in Equus. "I'm still getting naked questions about that," he says of the 2007 play.
Numerous Harry Potter films followed, but the role marked his move from child wizard to adult actor. In that year, he also appeared in Australian film December Boys and TV movie My Boy Jack, alongside Carey Mulligan.
In 2011, the year that the Harry Potter finished, he made his Broadway debut in the musical How To Succeed In Business Without Really Trying, followed by the big screen horror The Woman In Black and the first series of A Young Doctor's Notebook in 2012.
He works hard - at one point he was filming A Young Doctor's Notebook during the day and starring in a Martin McDonagh's play The Cripple Of Inishmaan in the evenings. He says, grinning: "I only get tired if I'm bored. If I stop getting stimulated I shut down, I'm like a dog in that way."
Energy and enthusiasm aside, it must have been daunting to leave the cocoon of Harry Potter.
"You definitely have a moment of fear," he confesses. "But I never considered that I might not have a future in the industry until I was asked that by a journalist.
"You can react to that in one of two ways. One is to give up, the other is to use it to fuel you and prove those people wrong."
To a certain extent, he says, he's achieved that. "I'm on my way to it. I've done work I'm proud of but don't think it's the end of the process."
Kill Your Darlings is out now