I am America. I am the part you won’t recognise. But get used to me. Black, confident, cocky; my name, not yours; my religion, not yours; my goals, my own; get used to me.

Muhammad Ali 1964.

SOON after he was crowned heavyweight champion of the world, Muhammad Ali arrived in Scotland on a promotional tour. He had only recently abandoned his Christian birth name, Cassius Marcellus Clay. It was a time of new names, Ali arrived at Renfrew Airport which a week later would become Glasgow International to be ­greeted on his arrival by the Braemar ­Ladies Pipe Band of Coatbridge.

Kitted in kilts and playing the pipes and drums, the band charmed and mystified the bewildered visitor.

Ali was in Scotland to fight at an ­exhibition bout at Paisley Ice Rink, where he fought his sparring partner and long-time friend Jimmy Ellis. Both boxers were going through the motions for money, but beneath the hype and fake rivalry, their friendship was the stuff of Netflix movies. Jimmy Ellis had been at school with the then Clay at Central High School in ­Louisville, where they were part of a quite ­outstanding team of teenage fighters from Kentucky who travelled north to Chicago to dominate the Gold Gloves tournament in 1958.

It is impossible to over-exaggerate their achievements. It’s like a school football team from Peebles destroying the best that the central belt has to offer and ­leaving Glasgow with the medals. Ali’s friendship with Jimmy Ellis was astonishing too. Ellis was a profound and deeply religious teenager, himself a gifted gospel soul singer, who eventually signed for Atlantic Records later in the 1960s.

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One of the unwritten rules that Ali ­insisted on when he joined the Nation of Islam was that no one was to intimidate Ellis for being Christian, that he should not be pressurised to convert and that he should be allowed to practice his faith unmolested.

In the late 1960s, when Ali was stripped of his title for refusing to be drafted to fight in the Vietnam war, Ellis rose through the rankings and in 1968 became heavyweight champion of the world in place of his friend.

Some have claimed he always lived in Ali’s shadow, but what they fail to say it was the most dynamic shadow ever cast in the history of professional sport.

By his own account, and by the many millions who adored his unique ­personality, Ali was quite simply the greatest. On his visit here, he posed ­naked to the waist in a kilt, sporting a glengarry bunnet and charmed the crowds. It remains one of the greatest photos of celebrity Scotland, only – rivalled by The Beatles at the “Haste Ye Back” sign at the ­English border or Ali’s nemesis ­Sonny ­Liston, who also ­visited Scotland on the ­exhibition circuit, ­marching along Glasgow’s Gordon Street in full ­highland-dress.

Later this month a film based on my book Cassius X, opens at the Glasgow Film Festival. It focuses on that brief ­period in the life of Ali, when he trained in Miami and was converting to Islam.

The book tells of the influence of two men – both called Sam – who helped shape Ali’s unique approach to life.

Ali’s friendship with Sam Cooke burned bright at a time when black ­music was at a crossroads: gospel was spilling from churches across the nation into the bedrooms of the young, transforming love for the Lord into a more sexual and secular kind of romance.

Cooke gave birth to a new form of ­music but more importantly to a new way of ­doing business, pioneering his own ­labels, running his own management agency, and controlling his own ­publishing ­copyright.

By the time Ali met Cooke, there were numerous successful African American businesses, in pharmacy, the funeral trade and local taxi firms, but it was in entertainment where the aspiration of ownership and self-reliance was most dramatic.

In the soul studios of Detroit and the gospel stores of Chicago’s Southside, Cooke and his contemporaries were very public exponents of taking control. It was a message that Ali began to apply to his own life and to the tensely criminal world of boxing.

MOST important of all his acquaintances was a squat man called, Sam Saxon, a former pool-hall hustler who moved to Miami and ran the toilet and shoe-shine concessions at Hialeah Racetrack.

Saxon was something more than a ­shoe-shine boy, though. He was a ­renowned street captain of the Nation of Islam, sent to Miami to recruit young men in the dilapidated streets of the Overtown ghetto and to offer hope to the ­ex-prisoners from the “Flat Top” in ­Raeford Prison who had drifted back to their old haunts.

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Saxon had converted to Islam as a ­teenager and was valued as one of the ­Nation’s most successful “fishers of men”. It was Saxon who first invited him to ­cancel his slave name and adopt the temporary alias Cassius X.

They met regularly in a darkened room, behind the sun-parched blinds of the Sir John Motel, as guests and visiting soul musicians lounged by the pool. It was in these inauspicious settings that Saxon laid the first paving stones on Cassius’s path to Islam and his historic ­transformation into Muhammad Ali.

According to Saxon’s recollections: “My job was to see that that the men in the Temple were trained to be good ­providers for their family, made ­physically fit, and taught how to live right … There weren’t many members who attended regularly. Realistically, in Miami there were only 30. I met Ali in the March of 1961 when I was selling Muhammad Speaks ­newspapers on the street. He saw me, said, ‘Hello, Brother, I’m Cassius Clay. I’m going to be the next heavyweight champion of the world’.”

Cassius was nervous about the impact on his boxing. “For three years I’d sneak into Nation of Islam meetings through the back door. I didn’t want people to know I was there. I was afraid, if they knew, I wouldn’t be allowed to fight for the title but the day I found Islam, I found a power within myself that no man could destroy or take away.

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“When I first walked into the mosque, I didn’t find Islam … it found me.’ When Ali came to ­Paisley journalists and cameramen flocked round him there were two life defining stories that they could have told. The first was the remarkable friendship with his ­sparring partner, Ellis who for the ­theatrics of the occasion was portrayed as his sworn ­enemy.

Then there was the astonishing ­journey of faith that had fastened Ellis ­unshakably to his gospel roots and the different path that had taken Ali on the less ­conventional and more controversial journey towards the Nation of Islam.

Reflecting on Ali’s visit to Scotland, it came at a crucial moment in his career as mainstream America retaliated against his exuberant success. In Scotland it was one of missed journalistic opportunities. If only Hugh McIlvanney or Ian Bell had been in Paisley that week something of lasting analytical value might have emerged. But this was tabloid Scotland in the early 1960s, so they fitted them in kilts and encouraged them to clown around for the cameras. Muhammad Ali was busy fashioning a career enriched by showmanship, so he did exactly as they asked. He clowned around and his reputation grew. Then came Vietnam.

Stuart Cosgrove’s book Cassius X is published by Polygon and a feature film based on the book open at the Glasgow Film Festival and will be screened on March 9, 10