FEW names carry as much weight as Muhammad Ali – so it’s no surprise his son and heir faced an epic fight to live up to his legacy.

Not only was the late legend considered to be “The Greatest” boxer of all time, he had a ­magnetic personality and a moral purpose championing his anti-racism campaign in the US.

It was therefore inevitable that his namesake, Muhammad Ali Jnr, had high expectations to meet.

But the younger man had struggles of his own, ending up hooked on drugs, surviving on food stamp benefits and living in a leaky hovel — cut off from his famous father.

The 50-year-old American has now cleaned up his act and will be the subject of both a documentary and a dramatised movie.

The films will delve into the trials of being the offspring of Muhammad Ali — born Cassius Clay — probably the world’s best-known athlete.

While you might imagine that Ali Jnr would have been brought up in the lap of luxury, he was in fact raised by his grandparents, who struggled for cash.

And while he could have chosen to adopt his dad’s birth surname of Clay, he stuck proudly with Ali.

Speaking exclusively to The Sun, he says: “I was born with the name Muhammad Ali, so I had to be protected because, later in life, my father said, ‘This is Muhammad Ali — when I’m done, he’ll take over’.

“Now I’m taking over the legacy. I’m going to keep the legacy going. I am Muhammad Ali Jnr.”

Ali Snr was 25 and already a divorcee when he married Jnr’s actress mum, Belinda Boyd, in 1967. She was aged just 17.

‘My father was just a teddy bear’

They had three daughters, Maryum, Jamillah and Rasheda, before the boxer’s male heir arrived.

By this time, Ali was known the world over thanks to his quick feet, devastating glove work and his refusal on conscientious grounds to fight for the US military in Vietnam.

But with fame and fortune came the attention of numerous women — a temptation he could not resist.

He cheated on Belinda, who changed her name to Khalilah Ali, before leaving her for his third wife, Veronica Porche, when Ali Jnr was four years old.

Ali Jnr reveals that messing with his mum was a bold move — because she was one of the few people to ever floor the champion.

He recalls: “I once said to my father, ‘Of all the fighting you did, what was the one fight you’d never do again?’ He thought for a minute and said to me, ‘Your mother’.”

That was because she had thrown him to the ground with a thump in a judo move when he’d crept into the house behind her.

After the divorce, Ali Jnr went to live with his maternal grandparents and would only stay with his dad during school holidays.

But his dad, who had at least nine children, made sure those visits were very special.

Ali Jnr says: “He would take us everywhere. It was all good back then. My father was basically a teddy bear.

“He loved his kids and he’d do anything for us. I never got spanked by him.

“It was someone we called ‘Daddy’ — I don’t know any other way to put it. He was a good father even though he wasn’t always there for us.”

The lack of contact with his children was something that the boxer came to regret. He warned Ali Jnr, “Don’t make the same mistake and same decision I made in my life”.

His son took the message to mean “having too many women and being with other women. And also the mistakes he made of not being there for his children”.

Despite earning a fortune from bouts — including the $100million 1974 Rumble In The Jungle against George Foreman — Ali Snr did not provide enough cash to support all his kids.

Ali Jnr says: “He was away a lot, so our grandparents raised me when I was a child. My grandfather was going to retire, but he had to work to pay the bills, the mortgage.”

Carrying the name Muhammad Ali around the school playground also proved to be a curse for his son.

He says: “I got bullied because the other children wanted to know if I could fight like my dad.

“I never showed my technique to anybody and I never will.”

Ali Jnr was more fearful about what might happen to his father as the older man stood up for the rights of black Americans, making him a target for right-wing groups.

Ali Jnr states: “I thought he was going to be martyred like Martin Luther King was.”

His dad also warned him about the dangers of a professional boxing career and Ali Jnr decided not to follow the same path. It was a wise decision in terms of health, because repeated blows to the head left the heavyweight king with Parkinson’s disease.

The brain damage meant that Ali Snr was so forgetful he once abandoned his son at a roadside eatery when the boy was 14.

‘I used to smoke weed, crack and cocaine’

Ali Jnr says: “One time my father picked me up from where I was living in Chicago to go to his home in Michigan and we stopped at a place on the way.

“He told me to go get something to eat and when I came back, he was gone. It was scary. I was crying.”

Around this time, Ali had married his fourth and final wife, Yolanda Williams, who is better known as Lonnie. After that, the boxer and his eldest son drifted apart. Lacking purpose and unable to escape his father’s shadow, Ali Jnr started taking illegal drugs.

He admits: “I used to use weed and smoke crack and heroin.”

In 2005 he married Shaakira and they have two children, Ameera, 14, and 13-year-old Shakera.

Ali Jnr says: “It was hard financially. I actually had to sleep on the floor because from my bed every day, every night, you would hear gunshots going off.

“Beside the crime, the water wasn’t right, the electricity wasn’t right, the building wasn’t right. When it rained it leaked into the room.”

Financial worries only increased the tension with Lonnie, who was his dad’s primary carer.

His son claims: “I asked him for some money. And she told me not to ask him for money. I really hated her for that.” Eventually, Ali Jnr began taking positive steps and quit his drug habit. He says: “I got off that and turned my life around. I stay away from drug addicts now.”

But marriage to Shaakira did not survive that turbulent existence and the couple are working out a divorce.

For a long time he was either unemployed or doing odd jobs, such as painting and decorating.

Recently, he helped set up The Muhammad Ali Legacy Continues, an organisation that aims to establish gyms in his father’s name and to campaign against bullying.

Much of his time at the moment is taken up with the movie projects. The documentary, My Father Muhammad Ali, is due out in here in March and there are plans to make a dramatised version of Ali Jnr’s life.

He reveals: “A biopic is going to start filming on my life story later next year by the same producer who did The Irishman with De Niro.” Ali Snr died aged 74 in 2016, but his son was left upset by the high-profile nature of the funeral, which was packed with celebrities. He says: “It was like a circus.”

There seems little point in Muhammad Ali Jnr trying to escape his father’s name — because his legacy is all round.

He concludes: “Everywhere I go, somebody has heard of Muhammad Ali and everywhere I go I see a picture of my father somewhere.

“It’s now like a dream. I never thought my father would die.

“The greatness he had, I never thought he would literally die.”