Rodney King ponders the question in silence while absent-mindedly rubbing the scar on his left hand, a big, black weal that spreads across the knuckles towards his wrist. "No," he says. "It's not painful to relive it. I'm comfortable with my position in American history." Then, the interview barely begun, he appears to correct himself and without warning reaches into his memory's darkest recess. "It was like being raped, stripped of everything, being beaten near to death there on the concrete, on the asphalt. I just knew how it felt to be a slave. I felt like I was in another world."

The words hover, incongruous, because it is a bright afternoon, in a chic restaurant and a jarring change of tone. King gazes at nothing in particular. The moment passes. In a lighter voice, he reverts to his original train of thought. "I know and value what it means to wake up and be alive and to share my story. I'm so blessed to be here and to be able to talk about it." He smiles uncertainly.

"It", of course, refers to the night of 3 March 1991 when four members of the Los Angeles police department surrounded and repeatedly beat the prostrate King by the side of a highway. Fifty-six baton blows and six kicks, it was later established in frame-by-frame analysis. This was before mobile phones with cameras, but from his balcony George Holliday, a plumber woken up by sirens, recorded it all on video camera. He passed the grainy, amateur footage to a local TV network, KTLA, setting in train a series of events that gave King, as he puts it, a position in American history.

This week, two decades later, finishing a risotto and sipping tea on a deserted restaurant terrace in west LA, King insists he is reconciled to the role. In reality, he and the country are both still grappling with it. Too much has happened since – or too little, you could argue – for it to be otherwise. A black man is president but black men are still disproportionately likely to end up jailed. Or, like Trayvon Martin, the teenager gunned down in Florida, dead. "When I see him scream, I hear the same scream I gave on 3-3-91," says King. "It's the scream of death."

The 47-year-old former labourer is an elusive mix. Physically imposing, 6ft 3in and with a powerful torso, he is nonetheless timid and walks with a limp. In his white shirt, snazzy tie and dark trousers he could pass for a businessman, save for the necklace of red and black beads. He made it himself. "It helped pass the time." He makes dramatic declarations and shows flashes of insight and humour amid half-sentences whose meanings shimmer and scatter like fish in cloudy water. Patchy concentration is the result of brain damage from the beating, he says. Decades of alcohol abuse and numerous car accidents have not helped. "Um, where was I?" he asks, losing the thread at one point.

We had been discussing the riots that bear his name. This week is the 20th anniversary of the explosion of rage that destroyed much of Los Angeles and shook the US after a near all-white jury acquitted King's uniformed assailants. Resentment in LA's black community had built for years over poverty, unemployment and police brutality. The acquittals on 29 April 1992 ignited a week-long, apocalyptic bonfire. "I put on my reggae hat with braids so nobody would recognise me and drove into the city to see what was going on," recalls King. "It was just …" the voice trails off, defeated by the magnitude of what happened. By the time the riot ended, 53 people were dead, thousands injured and $1bn worth of property smouldered in what could have passed for Bosnia.

It was partly thanks to King that the rioting did end. On the third day, he made a famous, tearful plea to a forest of microphones: "Can we all get along?" It was a challenge to two centuries of fraught race relations – still resonant in the Obama era – that established King as more than just a victim. Until then, he said, he had felt humiliated. "For a man to beat you so badly, till you're near dead, takes everything from you." He did not get to testify at the officers' trial. "It was like the lawyers wanted all the attention." It all changed, he says, when he intervened during the riots. "When I said 'Let's all get along', that was the start of my redemption right there. All the butterflies came out of my stomach."

The son of a violent, alcoholic father, King drank too much from a young age and had been jailed for threatening a shopkeeper with an iron bar. On the night of the beating, he was drunk at the wheel of his car and speeding. The police officers who cornered him after a dramatic chase said he resisted arrest and appeared dangerous. In a second trial after the riots, two officers, Laurence Powell and Stacey Koon, were convicted of civil rights offences. In a civil suit against the city of Los Angeles, King was awarded $3.8m (£2.3m), offering hope of a new start. Instead, his drinking grew worse, he was convicted of spousal abuse and repeatedly crashed his car, breaking his pelvis and giving him a limp.

The police beating of Rodney King, captured on video tape by George Holliday on 3 March 1991. Photograph: George Holliday/AP

Detailing this grim catalogue King, for a moment, turns mischievous. "When I see a uniform, I still get nervous but you know, when the police [he pronounces this poh-lees] pull me over and see it's me, they get even more nervous. They shake like this" – he trembles a hand. He grins, and this time the smile reaches his eyes.

When not watching television – the Discovery and History channels and cartoons are his favourites – King found himself on it. He participated in a celebrity boxing match and two celebrity rehab programmes, each time claiming victory, only to lapse back into the alcoholism that ruined relationships and turned his Rialto home, on the outskirts of LA, into a tip.

Now he is proclaiming deliverance in a book, The Riot Within: My Journey from Rebellion to Redemption, ghosted by Lawrence Spagnola, which is published to coincide with the anniversary. The last three chapter titles are: A new man; Clean and sober; Live, learn, love. King, in other words, has finally found peace. "This book is my testimony," he says. "I tell myself time heals. It really does." He places his case, which prompted a clean-up of the LAPD, in a continuum of racial landmarks from the abolition of slavery through to civil rights and Obama's election. "They all built on each other. Action and reaction."

As he sips tea and reflects on those who beat him, a happy ending seems to glimmer. "I had to learn to forgive. I couldn't sleep at night. I got ulcers. I had to let go, to let God deal with it. No one wants to be mad in their own house. I didn't want to be angry my whole life. It takes so much energy out of you to be mean." He relaxes by fishing, a passion imparted by his father. "Dropping that pole in the water and just waiting for that bite … ahh." There is even romance. King is engaged to Cynthia Kelley, a juror from the civil trial.

LA, to an extent, has also been redeemed. Racial tensions have ebbed, crime has tumbled, the police have reformed and there is a growing black middle class. It would be nice to leave it there. But the city, like King, is ambivalent, full of light and shade. Poverty and unemployment still plague a black underclass. Inequalities are widening, not narrowing. Parts of south central LA remain covered in rubble and weeds from the riots.

King himself remains a forlorn figure seemingly trapped by his past, his name and his addiction to alcohol, all, in his mind, inextricably bound. "I still suffer from headaches and nightmares. Flashbacks. I wake up with aches and pains. So, you know, it's nice to have some help." Meaning booze. In his book, he admits to being an alcoholic. In person, he elides the label. "Everyone is different. No one alcoholic is the same. I still drink … but I sip now. I don't drink for the buzz or to get drunk. I drink because I like the taste."

He plays down the self-destructive vortex that cost him family, health and savings: "I made some little childish decisions." Alcohol, he says, draining the tea, fidgety and anxious to wind things up, will not destroy him. "I've quit many times before." The interview ends.

One final question. What would he like to do in the future? King pauses. "Construction maybe. It'd be good to build something solid, you know, something that'll be there for a hundred years." He stands up, extends a handshake and heads out, limping slightly, into an overcast afternoon.