When Kenneth Branagh burst on to the scene 20 years ago he was the golden boy who could do no wrong. But then as his glittering showbusiness marriage crumbled, so did his career. Now he's back on top.

As comebacks go, it is very Kenneth Branagh. After several years in the wilderness of mediocrity, making a couple of indifferent films and a few truly ghastly ones, the Golden Boy of British acting is back in the sun again, his sheen more burnished than ever.

It has been an extraordinary 48 hours for Branagh. It began on Sunday when he won a best actor Emmy (the Oscar of the television world) for his powerful performance in the made-for-TV movie 'Conspiracy'. He had not travelled to Los Angeles for the ceremony, only because last night saw the opening of his new West End venture as director of 'The Play What I Wrote', which has already won praise from preview audiences.

To cap it all, the day after the premiere of the hottest movie of the year, production began on the second Harry Potter movie, in which Branagh will play smoothie villain Gilderoy Lockhart.

How very Ken to come back firing on all cylinders on both sides of the Atlantic.

Those glittering 48 hours follow six or seven rather drab years during which Branagh seemed capable of making only bad moves in both in his career and personal life.

It takes a certain kind of arrogance to write your autobiography when you're only 28 but that's what Ken did, without a flicker of embarrassment - even though he said it was purely a means to an end. He needed funds for his theatre company and penning the story of his life so far seemed a quick way to get it.

A few years later, when he was in his 30s, things started to go pear-shaped. the more he matured in stature as an actor and director, the worse his choices became - from the barely average to the downright abysmal.

Then, just after the release of his biggest turkey, the overblown 'Mary shelley's Frankenstein', which was full of enough ham to supply a streetful of delis, came the announcement of his split from Emma thompson, the Golden Girl of British acting.

Those who had gasped in envy at the young man whose precocious achievements actually warranted a book at 28, were sniggering that it was a good thing he had written it when he could still end it on a high note.

Precocity, the flipside of youthful brilliance, has dogged the Ulster-born Kenneth ever since, straight from RADA, he burst on to the London stage in the play, Another Country. He was 21 and not a conventionally handsome leading man but he had a dazzling rawness that eclipsed all others on the stage with him.

Kenneth was just 23 when he played Henry V, Shakespeare's most stirring young male role, with the Royal Shakespeare Company, and was hailed as the new Olivier. Indeed, there was something about the thin-lipped intensity which called the great Sir Larry to mind.

Only two years later, Branagh formed the Renaissance Theatre Company, with fellow actor David Parfitt (who played Wendy Craig's younger son in the Seventies sitcom And mother makes three).

It is not unusual for young acting buddies to get together and set up their own theatre companies to put on plays on a shoestring in out-of-the-way places; it's a way of keeping busy until the break comes along.

It is highly unusual for such companies to persuade the likes of Sir Derek Jacobi and Dame Judi Dench to work with them as actors and directors, but Branagh managed it. His energy seemed inexhaustible. In interviews, he talked like a machine-gun, firing good-natured expletives all over the place.

His friend Stephen Fry once said Branagh was the only person who could make him "vomit with laughter".

As well as running Renaissance, he starred in the film version of 'Henry V' and in the acclaimed television series 'Fortunes of War', where he met Emma Thompson, an actress-comedienne whose star was also very much on the rise.

Ken and Em went together like peaches and cream or Taylor and Burton, so perfectly matched in ability, talent and quirky attractiveness that even their names rhymed.

They were the icons of Eighties' luvvie culture and married shortly after a joint West End run in John Osborne's 'Look Back in Anger'. They couldn't, it seemed, put a foot wrong ... except when they stepped out on screen together.

'Dead Again' in 1991 was a curious mish-mash of camp film noir and gumshoe detective thriller, directed by Branagh. Even more curiously, he and Thompson played their roles as Americans with less-than-perfect accents. It did not do well.

'Peter's Friends' (1992) was altogether more familiar fare; Ken and Em and several of their mates - Stephen Fry, Hugh Laurie, Imelda Staunton and Em's mum, Phyllida law - all playing a bunch of chums acting daft in a big house in the country.

Branagh's next project, a lush production of much 'Ado About Nothing', filmed in gorgeous Tuscan landscapes with lots of hey-nonny-no-type frolicking, displayed Branagh as his "Renaissance Man" best. He directed, produced, starred in and adapted the screenplay for the film.

Hollywood also loved Ken and Em, the golden couple. Branagh's currency was high - Keanu Reeves, Denzel Washington and Michael Keaton had all come on board for 'Much Ado' - and now he went off to make 'Mary Shelley's Frankenstein', with none other than Robert De Niro playing the monster.

Off screen it was curtains for the Ken and Em marriage. Branagh, who was said to be as energetic in his love life as in his career, had cast the wraith-like Helena Bonham Carter in 'Frankenstein' and the pair fell for each other like a ton of bricks.

The break-up affected Thompson so badly that she barely worked for a year and admitted that questions about the marriage gave her "insomnia and nightmares".

Branagh and Bonham Carter made ludicrous attempts to keep their relationship secret but, by the time the film released, the cat was out of the bag. The movie, whuch was Branagh's biggest budget movie venture so far, bombed. Shortly afterwards - after picking up her first Oscar - Thompson confirmed the marriage was over after barely six years.

For Branagh, however, now aged 34, it seemed to herald much more: the loss of his Midas touch. His next project, 'In the Bleak Midwinter', was deemed no more than so-so.

He returned to Shakespeare, playing Iago in the film of 'Othello' in 1995, and 'Hamlet' a year later, but aroused little enthusiasm. 'The Theory of Flight', a movie he made with his new love, in which Bonham Carter played a woman with cerebral palsy, was remarkable only for its weirdness. Not even Woody Allen, who cast Branagh in 'Celebrity', could re-light the touch-paper for him. Not long after a tearful Helena confirmed her reationship with Branagh was over.

When he was presented with the Gielgud award for services to Shakespeare last year, the atmosphere at the ceremony in London was of a luvvie fest for someone who, although not yet 40, had his best behind him.

And the, last December, Branagh did hit 40 and also seemed to hit his stride again. He was a hugely popular choice in the Emmys for his performance in 'Conspiracy', in which he plays Reinhard Heydrich, the man behind the Nazis' Final Solution. The role in Harry Potter II, 'The Chamber of Secrets', came about because Hugh Grant pulled out. While Lockhart is not a large part, it will earn Branagh a £1 million pay cheque and, if the furore surrounding the first Harry Potter movie is anything to go by, exposure in a guaranteed blockbuster sequel. Along the way, he has also played the hero polar explorer Sir Ernest Shackleton.

But it is at Wyndhams Theatre that Branagh might well take his last steps to full rehabilitation as a giant of British acting. 'The Play What I Wrote' is an affectionate evocation of the Morecambe and Wise Show.

Just as such stars as Glenda Jackson, Tom Jones, Vanessa Redgrave and Shirley Bassey came on to the TV shows to have the mickey taken out of them in Ernie Wise's "plays", so the celebrities of today are clamouring for the privilege of being ridiculed in Branagh's production. There will a new celebrity guest each week and some will appear for only one or two performances, accodring to their availability.

Victoria Beckham is rumoured to be already pencilled in for next spring. Others keen to make time in their schedules include Kylie Minogue, Richard E. Grant, Jude Law, Sean Connery, Frank Skinner and Sue Johnston (from The Royle Family), as well as old Branagh cronies Jacobi and Brian Blessed. the changing guest spots mean that the play will be different from week to week or even from night to night.

It is the type of innovative twist which made Branagh's reputation. Not for nothing did he name his theatre company Renaissance 15 years ago. The word, after all, literally means rebirth, as well as carrying the figurative connotations of a new flowering.

Watch out for the rebirth and the re-blooming of Ken Branagh, renaissance man.