In 1968 he raised his fist and helped make the Olympic podium a political one - and he is determined to keep the flame alive

Meet half of sport's most rousing double act. John Carlos and Tommie Smith were the 200-metre dashers behind the most iconic image of the umbilical link between the competitive arts and political reality: the "Black Power Salute" in Mexico City that seared through the 1968 Olympics like a 1,000-volt bolt, electro-shocking millions watching the first Games to be televised live.

The legacy, however, is complex. If they hadn't flung open the doors for those seeking to better society from an Olympic platform, would 11 Israelis have been killed in Munich four years later? Would gunmen be preparing to occupy London's rooftops? Yet perhaps even the most hideous prices are worth paying for freedom of speech. Besides, if Elvis Presley hadn't ignited rock 'n' roll, somebody else would have.

To Harry Edwards, linchpin of the Olympic Project for Human Rights that Carlos helped launch and whose badge he and Smith wore, the protest was "inspirational". Brent Musburger denounced them as "black-skinned stormtroopers" and became one of America's best-paid broadcasters. But the salute wasn't solely about black empowerment. Smith raised his black-gloved right fist as a symbol of precisely that but Carlos hoisted his left, to celebrate unity. He left his tracksuit open as a salute to Harlem's underclass, "to black and white".

To Jesse Jackson it was "a statement for the ages... an act of righteous defiance". Inevitably, the US establishment let rip with both barrels. "Angrier, Nastier, Uglier" sneered Time magazine. Avery Brundage, the ancient IOC emperor, anti-semite and Nazi sympathiser bent on insulating the Games from the meddlesome tentacles of the real world, saw only "warped mentalities and cracked personalities". Carlos calls Brundage "sport's J Edgar Hoover".

Nor was every African-American a brother. When George Foreman began his climb to fame, glory and grilling-machine fortune by winning the heavyweight boxing gold that October, he waved a miniature Star-Spangled Banner. For all his dignity, Carlos still bristles at Foreman's anti-solidarity, at Brundage's anti-humanity.

He is still strident and straight-backed, but a ligament problem impairs his walking. Fresh in from California, he is here for a tour taking in Brixton, Broadwater Farm and East Sussex, to promote The John Carlos Story with Dave Zirin, the co-author who has been lauded by the Washington Post as the "conscience of American sportswriting".

To spend 36 hours with this wise, laconic and vibrant sexagenarian is to enter the set of Woody Allen's Midnight in Paris. Time spools back, scenes are expertly plotted and you can't see the walls for legends. But instead of a Jazz Age bash with Ernest, Salvador, Scott and Zelda, the party is full-on Sixties and strictly black and white. Meet Ali and Miles, Malcolm X and Martin Luther King: the pillars of African-American resistance. Carlos has every right to be at their shoulders.

The defiant ones paid dearly. "Including Peter Norman," Carlos stresses, underscoring the role played by the silver medallist who was ostracised in his native Australia, whose 2006 funeral the two Americans attended as pallbearers.

In 1968 Brundage ordered them home, to death threats and dead ends; work came grudgingly. Shadowed by the FBI, Carlos resisted an invitation to become a drug dealer and resurfaced as a high-school guidance counsellor. Then, on the 37th anniversary of that historic night, a statue of the salute was unveiled at San Jose University, propelling him from his shell.

He has but one regret: "I knew I'd cope, man, but I never considered the impact on my family." It contributed, he feels, to his divorce and hisex-wife's suicide. No less heartbreaking is the rift between him and Smith. After Carlos claimed he could have beaten his co-conspirator to the gold, Smith took extreme umbrage, hitting back with interest. Carlos discusses it gingerly: the scars run deep. Smith, he reasons, "had trouble sharingthe recognition".

To enlighten and rouse other generations: that is the motivation now. Being a gifted storyteller bridges the gap, the account of Carlos's1967 meeting with Dr King almost unbearably poignant.

"Why are you backing the proposed Olympic boycott by the OPHR?" wondered the fearless 22-year-old. "He said it was like throwing a stone in the water and seeing it ripple to the edge. Then I asked why he was going back to Memphis, where he'd already had death threats. His reply never leaves me: 'I have to go back and stand up for those that won't stand up for themselves, and for those that can't stand up for themselves.'"

His sporting role models were "Jackie and Jack", Robinson and Johnson. The first African-American to play major-league baseball in the 20th Century, Robinson took his boots to Carlos Snr, a Harlem cobbler. What tattooed itself on his son's consciousness was the Brooklyn Dodger's courage. "Jackie had the balls, the balls to take everything they threw at him." Ditto Johnson, the first black heavyweight world champion. "Jack was more in your face. Think about it. It's 1910 and you're the first black sporting champion. And you like white women. To put up with all they did to him and still come out fighting – maan, that takes balls."

He had the balls too. Still does. The anger's gone – "You can't win angry, can you, man?" – but the fire is nowhere near out. As he states in his book: "I still feel the old impulses, the old compulsions, to stand up and be heard, no matter the price." The inscription inside my copy is his mantra: "We live to make history".

The salute was about more than Vietnam or King's assassination or the Tlatelolco Massacre of hundreds, maybe thousands, of Mexican students a fortnight before.

"It was about the stories my father told me about fighting in the First World War. It was about the terrible things he was asked to do for a freedom he was denied when he returned home. It was about him being told where he could live, where his kids could go to school, and how low the ceiling would be on his very life."

He was cheered at Occupy Wall Street, and that sense of duty endures: the need to keep on keeping on. Bring up Michael Jordan and Tiger Woods and Carlos defends their right to enjoy the fruits of resistance while excusing themselves from the front line, though he does wonder "what they see when they look in the mirror".

Following an impassioned Q&A session for a packed house at the University of Brighton's Chelsea School of Sport, a small Twitter frenzy erupts among the students. Later, in Lewes, where Tom Paine conceived The Rights of Man, Zirin reads a tweet aloud, prolonging each syllable of "inspiring". The inspirer leans back in his chair, plainly touched. The next day's tutorials bring more of the same.

Being John Carlos may not be the easiest job in the world, but you suspect it is among the most spiritually rewarding.