To some he's the finest American actor of his generation. To others he's the ultimate outspoken Hollywood liberal, the guy whose political activism has defined him more than his films in recent years.
To the American tabloid media, he's been the gift that keeps giving, with a volatile love life involving Madonna (married for four years) and Robin Wright (married for 14).
He's now dating Charlize Theron who he's just directed in The Last Face, filmed in her native South Africa.
He might be all that. But right now Sean Penn, 54, is a recognisable rumble at the end of a phone line to somewhere on the Californian coast where he's spending the day staring at the sea and talking about his film The Gunman and a few tangential matters.
The interview comes with a repeated "no personal questions" warning from the film's publicity department. Which is amusing. Because you get the feeling The Gunman - an action flick from Pierre Morel, the man who turned Liam Neeson into an action hero in Taken - is possibly the least personal movie Penn has ever made.
Initially, it is set in a world Penn is familiar with, a world of aid organisations in Third World countries. So is The Last Face.
But in The Gunman, Penn plays a private security contractor, who might ostensibly be in the Congo to provide protection for charity workers, but whose firm offers political assassinations as an extra service.
Cue Penn taking out a local politician targeted by mining interests and fleeing the country, only to return years later to help out a NGO doing non-lethal aid work and find he's on someone's hitlist himself.
As Penn talks the movie's American release is still in the future. It has sunk largely without trace - and gone unloved by reviewers - at the US box office making just US$10 million.
So in retrospect, any questions about this being a career move, an attempt to start a franchise or just get in front of a big popcorn audience are slightly redundant.
Still, Penn is amusing when it comes to pondering things like his seemingly blockbuster-allergic career.
"I have always tried to approach what we call one's career without careerism - simply because I have to tell you I find myself talentless at careerism. And mostly because I have never known what part of it I have to be most interested in.
"That doesn't mean that I am not as hopeful as the conscious careerists in something doing well. I am. But the choices about making movies - once you have got your bills paid movies take too much out of you to do them for that reason."
At what point did he realise he wasn't any good at career stuff?
"Oh I can say there were many points where I realised that," he chuckles, "Asking me about why a movie is performing well or if The Gunman will perform well is kind of like asking a Taleban member to judge a dance competition. I am virtually the last person to ask."
"Many years ago there was a film called The Gumball Rally and the Italian driver jumps in the car and pulls off the rear view mirror and says 'what is behind us does not matter' ... once you have made your choice you just go with it.
"If it's embraced or it's not embraced. Or if it's successful or it's not successful. You put your best foot forward and then it's behind you and it's done."
Penn doesn't see playing a crackshot fighting machine as much of a departure from his previous work.
"Not really to be honest. You know the job of an actor on a movie doesn't change too much, movie to movie. [This one] had some very clearly tangible demands that are more things than I have done before but for me it is kind of a process question ... I didn't experience the departure.
"I understand the question. But it doesn't relate to what happens when you are making a movie."
And no he hasn't spoken to Liam Neeson about doing a Liam Neeson.
"No, but these are the catchphrases that I will grin and bear."
Well it doesn't look like Penn will be tooling up for The Gunman II any day soon.
He doesn't star in too many movies these days, with The Last Face his fifth film as director - but he's not up for talking much about the other film or its common ground with The Gunman.
"There are some superficial commonalities. Africa being one of them and NGOs being one of them."
Both movies star Javier Bardem. And of course, you have to mention in hope of breaching the personal stuff rule, that he has a very popular South African actress in The Last Face.
"Yes indeed we do," he says bluntly. If he's not exactly expansive on directing Theron, there are possibly other reasons. The film, which, reportedly has had a fairly messy genesis, was originally to star and developed by Robin Wright.
But talk about setting movies in developing countries at least lets us wander into wondering about Penn's real-world activism.
He's been on the frontlines in the wake of Hurricane Katrina and the Haiti earthquake. He's been visiting and shaking hands with politicians in Iran, Cuba and Venezuela in the past decade, much to chagrin of US Republicans, as was his criticism of George W. Bush over the invasion of Iraq and other matters.
Where does this born-and-bred Hollywood guy get the motivation for all that?
"I don't know I have ever been able to articulate an answer to that question. I feel clearly I am in a very lucky club.
"I am not a wealthy person but by world standards I am supernaturally wealthy. I have access to having my voice heard. I have experience in certain logistics and I am a citizen and I think whatever anybody can bring to the party, they should be bringing to the party.
"If I thought about this a lot it would make me very upset. But what I think is extraordinary is that everybody isn't doing it.
"Because I see people with less than nothing doing more than I am doing. So I almost get uncomfortable explaining why I do what I do ...
He must have developed thick hide for criticism over the years - not just for his movies but his efforts off screen too.
"Yeah I've got a pretty good one and I have a wall to kick when I don't.
"The good news is that most of the areas that need the most help have the least TVs, radio and magazine publications. So you tend to not be aware of the criticism while you are doing what you have to do."
Penn doesn't think he's as much of a lightning rod in the United States as he once was.
"There was a period of time I think around the Iraq war where that was certainly true.
"Yes I'm a go-to in that category. The thing that started everybody's lightning rod status for me was a letter I wrote to the Washington Post years ago and you go and read that letter now - even Fox News acknowledges everything I have said in that letter. What they do is so impulsive and of a moment and of a dogma that is not even sustainable in their own lives and their own position.
"So I am a short term lightning rod who keeps coming back as a short term lightning rod again and again."
Who: Sean Penn
What: The Gunman
When: Opens at cinemas today