Soon after Jada Pinkett Smith announced she was boycotting this year's Oscars because of the lack of diversity among the nominees, her husband Will Smith (along with director Spike Lee) followed suit.

After three decades in the business, as an actor, producer and musician, the 47-year-old - whose performance in new film Concussion has been cited as an example of how the Academy overlooks non-white actors - has always been vocal in calling for change.

In fence-sitting Hollywood, where even a slightly opinionated Tweet can divide fans and threaten your prospects, Smith has spoken out in support of same sex marriage, backed Barack Obama's presidency and in 1989, boycotted the Grammys - despite the fact he and music partner DJ Jazzy Jeff were nominated (and eventually won) the Best Rap Performance prize - because organisers refused to televise their category.

Recently, Smith said he was considering entering the world of politics himself.

"Well, you know, I was joking-ish, when I said it," he says with a smile, clasping his hands together in the manner of a seasoned politician.

"What happens is, as an actor, when you get to wear the life of a hero [in a film], it wakes up and it inspires things inside of you."

The latest character to do this is Dr Bennet Omalu, who Smith plays in new thriller Concussion.

A David and Goliath tale, it explores the true story of American immigrant Dr Omalu, a brilliant forensic neuropathologist who made an important medical discovery concerning the long-term impact of repeated concussions on football players.

"At the centre of this film is a man who was delivered a truth about a game that he had no connection to," explains Smith, who, despite pushing 50, still looks boyish in his burgundy polo shirt. "He had to deliver painful information to a group of people that he had a deep desire to be accepted by."

But his quest puts him at loggerheads with one of the most powerful institutions in the world, and he soon finds himself at the centre of a smear campaign intended to discredit him and his findings.

It's rousing tales like this that Smith is referring to when it comes to his own political ambitions.

"Dr Omalu has the immigrant's and the outsider's perspective of America," explains the actor, who has a son Trey from his first marriage, and two children, rapper Jaden and actress Willow, with Pinkett Smith.

"And if I felt the demand of what America is supposed to be and the ideals that were set forth by the forefathers that we have to live up to, even when we're fearful... You know, we can't get scared and then embrace our lower selves, so I feel like I have a distinct voice and a distinct opinion and a potentially useful set of skills to inspire people to reach for our highest American ideals."

Born in West Philadelphia, Smith kicked off his career as 'The Fresh Prince', performing as a rapper alongside old school friend Jazzy Jeff and scoring hits in Summertime and Boom! Shake The Room, before coming to wider fame in teen comedy The Fresh Prince Of Bel-Air.

He went on to save the world several times over in blockbusters Men In Black, Independence Day and Bad Boys - which is returning for a third and fourth outing in 2017 and 2019 - before tackling an altogether heavier role in 2001 Muhammad Ali biopic Ali, which netted him an Oscar nomination.

Concussion then, very much fits into that serious side of his professional coin. As well being gripped by Dr Omalu's story, as a parent of "big time football player" Trey, Smith was eager to learn more about the potential dangers linked with American football.

"It made me nervous that I didn't know [of the dangers]," says Smith, who was also Oscar-nominated for 2006 movie The Pursuit of Happyness.

"I was concerned about my son breaking his leg, my greatest concern when he was playing was spinal injury - but there was not one conversation, not one issue about long-term neurological repercussions. How could I possibly be a parent and have four years of football and no information?"

He's keen that others understand the potential repercussions of repeated concussion.

"Because I didn't know, I knew that other parents didn't know," he adds. "Part of the mission of this film is to deliver the information.

"It's not just American football. We're starting to see it in the repeated headers in soccer and we're starting to see it in Australian rules football and in rugby.

"I think it's really important that people have the information. People decide what they want to do, but they have to be coming from a space of knowledge."

Although football is part of the story, Smith immersed himself in the adversity and eventual victory Dr Omalu experienced.

"My focus is on Bennet and the pain and triumph of the story of an immigrant who came to America, suffered what he had to suffer, and ultimately was vindicated," he says.

"I look at this film as the close of a chapter for Bennet. This is a man who was born during an air raid in Nigeria. His mother was hit by shrapnel when he was being delivered. To go from there, to go through the suffering of bringing this story to the American public, and then to have your life story told through a Hollywood film - that's a beautiful hero's journey."

A worthy story, certainly. But if Concussion represents the serious side of Smith's working spectrum, his summer plans with Jazzy Jeff offer lightness.

"We're going on tour this summer," says the star, clapping his hands and laughing.

"We're going to go out there. I'm sure we'll be somewhere near your home town. I'll see you over there!"

:: Concussion is released in cinemas on Friday, February 12