Worse things can happen to a chap than becoming part of a hit TV show. But that sort of exposure can create an image that can be hard to shift. When punters welcomed JR into their own homes for more than a decade, for example, it became hard to accommodate the notion of a benign Larry Hagman.

Jim Parsons, a 41-year-old Texan in a neat suit, is not really Sheldon Cooper, the anal young physicist he plays in hit sitcom The Big Bang Theory, but I’m willing to bet fans occasionally make just that error. Am I being unfair to the enthusiasts?

“It’s hard to say. I never feel that they think I’m going to be a genius or a scientist,” he says. “But I do think that they are uncertain how unapproachable I am going to be. I am quite the opposite of unapproachable. When I moved to New York I had to steel myself to be a little less welcoming. But how could they know that?”

Parsons is, indeed, a friendly fellow, though not in a back-slapping, deep-chortle sort of fashion. Impressively urbane, endlessly well-mannered, surprisingly serious, Parsons comes across like a better-dressed creative writing teacher at an Ivy League university. Who better to voice a deranged alien opposite Rihanna’s perky heroine in this week’s charming animation Home?

“Oh, I found that heaven,” he says. “I really did. It was kind of the ultimate in creativity in a way I didn’t see coming. There is a level of playtime I hadn’t enjoyed since I was a child.”

Parsons is a keen analyst of the dynamics of fame. We meet at Claridge’s Hotel in London on a crisp late-winter afternoon. Such is the popularity of The Big Bang Theory – which finds Sheldon living with Johnny Galecki’s more socially adroit scientist – that there is barely a street where he’s not recognised. In London or New York, however, it is, apparently, usually tourists who shout catch-phrases at him; the natives are too cool. These incursions on privacy must be frustrating.

“I was very fortunate because I was in my early 30s when all this started,” he says. “I had a life outside this. I got to do so much living. So, when I was young, I was able to figure out all the usual things in peace. I figured out I was gay. I am so glad I wasn’t a child star and then had to figure out my sexuality in front of the world. It’s a little different now. But that would still be difficult.”

Officially straight

He raises an interesting point. We can all name prominent actors who, though officially straight, we suspect to be gay. But the atmosphere is changing. In the aftermath of The Big Bang Theory’s success, few outlets bothered to comment on Parsons’s sexuality. Those that did took a matter-of-fact tone. Things would have been different 10 years ago.

“I see no doubt about it. Just think about the tumult that Ellen DeGeneres encountered. So much has happened. You think: that’s quite a while ago. But it really wasn’t. I can think of few examples of social change that happened at that pace. Ten years ago I never considered the notion of marriage. That’s partly to do with who I am. But it wasn’t even on the table.”

Parsons is not wrong about the rate of social change in this area. He listens patiently as I talk him through the complications concerning our own upcoming referendum on same-sex marriage (I think he’d like you to vote yes) and raises a surprised eye when I point out that, just 20 years, a plebiscite to bring in divorce very nearly failed.

“What? What was that about? Really? Really?”

Asperger stereotype

The Big Bang Theory has attracted some controversy for its presentation of Sheldon as an uptight individual with traces of Asperger syndrome. Parsons has gone among physicists and has found them very supportive of the show. It is, however, hard to deny that certain stereotypes are being entertained.

“It’s a difficult question,” he says. “Very early on I was asked by a reporter whether Sheldon had Asperger’s. I wasn’t sure what that meant. I asked the writers and they said no. He has Asberger traits. But their saying that took away a social responsibility.”

At any rate, those occasional niggles have not stopped the show from becoming a genuine ratings sensation since debuting in 2008. Season one drew a perfectly decent average of 9.6 million US viewers. The last season hit a stratospheric 20.4 million.

Parsons is wisely not giving any firm clues as to when the show might end, but he reckons we will see another two seasons at least. The fanatical gaze of the digital eye will be on him throughout.

“I have kept myself shut off from the internet stuff,” he says cautiously. “Mainly because the personal connections with fans has always been so positive. I do have an Instagram account. I’ve allowed myself that.”

I think Jim Parsons will be fine. He has the clear eye and the confident timbre of an artist who intends to hang around a while.