'There are people, much more intelligent than me, who manage to sell an image of themselves, completely different to mine, but deep down they are the same as me.' Jose Mourinho about Pep Guardiola.

In his office at Real Madrid's Valdebebas training ground, Jose Mourinho used to keep a life-size cardboard cut-out of himself. It wasn't there for reasons of vanity.

The image was of Mourinho sprinting, finger pointing skywards, across the turf of the Nou Camp moments after his Inter Milan team had edged past Pep Guardiola's Barcelona in the semi-final of the 2010 Champions League.

Pep Guardiola (left) and Jose Mourinho are set to renew a long and eventful relationship

Real Madrid appointed Mourinho after he knocked Barcelona out of the Champions League

Mourinho's quest to break Guardiola's grip on Spanish football underpins a bitter rivalry

That two-legged victory, that proof that he could find a way to beat Guardiola's gilded team, was the reason Mourinho got the job at Real that summer. The photo was a reminder of why he had taken it. To knock Barcelona off their perch.

Mourinho's desperate quest to break Guardiola's grip on Spanish football underpins a deep and bitter rivalry between the two men that resumes at Old Trafford on Saturday in the colours of Manchester United and Manchester City.

Those who know Guardiola say that the relentless Mourinho onslaught on and off the field during two unprecedented seasons of unpleasantness and intrigue in Spain was a major contributing factor to his decision to quit Barcelona for a sabbatical in the summer of 2012.

When he walked away, Guardiola had an El Clasico record of W5 L2 D4 against Mourinho. Still, though, he is known to have confessed privately: 'Mourinho has won the war.'

Those close to Guardiola say his battle with Mourinho was part of why he took a sabbatical

How intriguing, then, to be reminded of another, earlier, chapter in the Mourinho/Guardiola story.

The time is May 1997 and Sir Bobby Robson's Barcelona have just beaten Paris Saint-Germain of France in the European Cup Winners' Cup final. On the field two men hug. One is Guardiola, the star of Robson's midfield, and the other is Mourinho, the great English manager's translator and confidante.

Mourinho was subsequently given a photograph of that moment. That one has never been displayed in his office but he has kept it.

'Yes, I still have a photo of that embrace,' Mourinho told Spanish television station Cadena Ser.

'We were close.'

Mourinho did admit that there was a time when he and old adversary Guardiola were close

In another world, Jose Mourinho could have been manager of Manchester City. His agent Jorge Mendes briefly courted the Premier League club as Roberto Mancini's title tilt threatened to derail in 2012.

He could have been manager of Manchester United a year later, pitching desperately for the job in the wake of Sir Alex Ferguson's retirement.

But the job the younger Mourinho really wanted, back in 2008, was the one at Barcelona and the fact he was overlooked for the less experienced Pep Guardiola lies at the very heart of an enduringly complex relationship between the two men.

Having worked under Bobby Robson at the Nou Camp, Mourinho vowed to return when leaving in 2000. 'Today and forever, Barca is in my heart,' he said.

Mourinho spent four years as a coach with Barcelona and vowed to return to the Nou Camp

GUARDIOLA V MOURINHO HEAD-TO-HEAD RECORD Games: 16 Guardiola wins: 7 Mourinho wins: 3 Draws: 6 Advertisement

Eight years later, Barcelona directors Txiki Begiristain — now of City — and Marc Ingla interviewed Mourinho in Lisbon. The recently deposed Chelsea manager told them that, if chosen to replace the departing Frank Rijkaard, he would promote a young Guardiola from head of the Nou Camp's B team to be his assistant.

What's more, Guardiola himself had already recommended Mourinho to the board. It seemed as though a relationship forged more than 10 years earlier was about to move to the next level.

'Jose had always recognised that Pep was an important figure at the club,' Robson told Patrick Barclay for his 2011 biography of Mourinho.

'He thought: 'I have to get in with this guy. I have to get to know him'. And he did. They were quite friendly.'

Mourinho was favoured for the Barcelona post in 2008 but Guardiola was given the job

Mourinho was favoured for the post in 2008 by several on the board ahead of candidates such as Arsene Wenger and the manager of Villarreal, Manuel Pellegrini.

But with Begiristain and Ingla wary of Mourinho's reputation for controversy, they were instead swayed by the recommendation of the creator of the modern Barca, Johan Cruyff. To many people's surprise, including his own, Guardiola was given the job.

'Mourinho is a bit poisoned by the fact he was rejected,' Ingla later said in Graham Hunter's book Barca: The Making of the Greatest Team in the World.

Mourinho may dispute that but few in Catalonia do. Leaving that aside for the moment, the hypothetical image of Mourinho and Guardiola working as one at the modern Nou Camp is a fascinating one. The pragmatist in harness with the idealist.

Barcelona legend and football icon Johan Cruyff recommended Guardiola for the position

Perhaps, with hindsight, the club missed the biggest trick of all eight years ago as, under Robson in the late 1990s, the makings of a relationship were clear.

'Mister Robson wasn't always as clear with the players as you would think,' one player from that era told Sportsmail this week.

'His instructions were not always understood but Pep and Mourinho would work together to fill in the pieces.'

At that time Robson would often outline his ideas in chalk diagrams on the concrete floor. Guardiola and Mourinho would bring those squiggles to life and some players even credit the pair with the tactical plan that saw Barcelona to victory in the 1997 Copa del Rey final.

'We would exchange ideas,' said Guardiola. 'It was a friendship, well a working relationship.'

Both Mourinho and Guardiola flourished under the tutelage of then Barca boss Bobby Robson

When Mourinho eventually returned to La Liga with Madrid in 2010, it was a relationship already under strain after Inter's fractious Champions League win the previous spring. Soon, it was to fall apart completely.

Having opposed Mourinho in the Premier League for three-and-a-half seasons, Ferguson warned Guardiola — only half in jest — at a coach's conference in Nyon that summer to: 'Prepare yourself, Jose is on his way.'

Guardiola replied that: 'It won't be so bad', a prophecy that turned out to be dreadfully wrong.

What followed over the next two seasons was as brutally ugly as it was hypnotic. The great Italian coach Arrigo Sacchi described having the two men in Spain as having 'two Picassos in the same period' but at times there was little pretty about the pictures they painted.

Barcelona won the first Clasico of the sequence by a crushing 5-0, a performance that brought United captain Wayne Rooney applauding to his feet in his living room. Subsequently, the teams met 10 more times in 16 months, including a spell in spring 2011 that saw them play four matches in just 18 days in league, cup and Champions League.

The first Clasico with Mourinho and Guardiola in charge ended 5-0 to Barcelona in 2010

After that sequence one Madrid player is known to have sighed: 'I am sick of the ******g Clasico' and this period is already cemented as one of the most seismic in the history of Spanish football.

Barca v Real. Cantera v Cartera (youth v the wallet). Guardiola v Mourinho. Whole chapters of books have already been written about it while Sid Lowe's history of the rivalry — Fear and Loathing in La Liga — is undoubtedly named after it.

The theorists will tell you that during that time Mourinho's whole self-image was constructed in defiance of Barcelona, the club that had said 'no' to him. He told his players, for example, not to mix with those from Barca while on international duty. 'They are not your friends,' he said.

What is clear is that under Guardiola and Mourinho the rivalry between the clubs became more visceral than ever. The two seasons' matches yielded 35 goals but it's the unprecedented level of rancour that stood out.

For his part, Guardiola considered Real brutish. Mourinho's team had a player sent off in each of the first four Clasicos of season 2010-11. Guardiola also thought Mourinho too eager to spread battle beyond the confines of the pitch and in to the press auditorium and the referee's room.

Guardiola did not like Mourinho's fondness to take their battle beyond the pitch

Mourinho, meanwhile, accused Barcelona players of play acting and suggested the Catalans were treated favourably because of the UNICEF logos on their shirts.

It was primitive and transparent and unattractive and not much of it was to do with the actual football. Certainly it was a far cry from the conversations the two men used to have on the quiet training fields of Barcelona, something that seemed to resonate more with one of them than the other.

On April 27, 2011, for example, Barcelona met Real in game three of the teams' infamous four-game sequence, the first leg of a Champions League semi-final that Guardiola's team were to win.

At his press briefing before the first leg at the Bernabeu, Guardiola ignored the calming advice of club officials to deliver a two-and-a-half-minute attack on Mourinho that later drew a standing ovation from his players.

Guardiola said he did not want to 'compete' with Mourinho in the press auditorium

Guardiola said: 'In this room, he [Mourinho] is the f*****g boss. I don't want to compete with him here.

'I would only remind him that we were together, he and I, for four years. He knows me and I know him. That's enough for me.'

Here, perhaps, is the difference between the two men. It is thought that Guardiola has struggled to separate the Mourinho he once knew from the Machiavellian caricature now so recognisable.

Mourinho, meanwhile, is less emotional. As he said once to Spanish journalist Lu Martin of El Pais : 'I don't waste time thinking about the people who love or hate me.'

What is important here is to recognise the power football at this level has to change lives, morph personalities and ultimately destroy relationships. It is this understanding, this background, that forges the ground on which Mourinho and Guardiola will stand in Manchester on Saturday.

Guardiola could not come to terms with Mourinho's complete change in character

Barcelona do not spend as much money on players as Real Madrid but they do spend money. Pep Guardiola spent £60million on Zlatan Ibrahimovic in 2009 and it proved injudicious.

Tomorrow the manager of Manchester City will face not only one brooding, familiar figure but two. Jose Mourinho has brought Ibrahimovic to Manchester and the Swede feels he has a point to prove.

Guardiola signed Ibrahimovic as part of a squad overhaul that saw the likes of Samuel Eto'o leave Barcelona but his two-season residency proved to be blot on an otherwise stellar career. The night Mourinho and Inter came to Barcelona to defend a 3-1 Champions League semi-final lead in April 2010 stands out.

Zlatan Ibrahimovic accused Guardiola of 'sh*****g himself in front of Mourinho'

Guardiola's team could only win 1-0, handing a place in the final to Inter. Subsequently, Ibrahimovic accused his coach of 'sh*****g himself in front of Mourinho'.

In his autobiography 'I Am Zlatan' the current United striker wrote: 'It was war and it was me against him, Guardiola the frightened little over-thinker who couldn't even look me in the eye or say good morning.

'I actually think Guardiola had a hang-up about Mourinho. Mourinho is a big star. He's the opposite of Guardiola. If Mourinho lights up a room, Guardiola draws the curtains. I guessed that Guardiola was trying to match up to him.'

Ibrahimovic started only 23 La Liga games in two seasons as Guardiola struggled to fit him in to a team containing the emerging Lionel Messi. Before long, Ibrahimovic was moved out to the wing.

Guardiola bought Ibrahimovic for £60m from Inter Milan but sent him packing after a year

One player who was a young squad member at the time told Sportsmail: 'Messi was the problem. He is more receptive these days to talented players alongside him but back then he didn't put up with any forwards really.

'If someone scored more than him or spoke more than him, they'd be in trouble. He was wary of Zlatan and was complaining all the time to Guardiola.

'Zlatan was a strong character, he joked with myself and all his team-mates and was liked by the squad. Of course he has an ego but at least he is transparent with it.

'Messi is different, he has his public face, all sweetness and light, as though he never says anything.

A former Barcelona squad member said 'Zlatan lost out' because 'Guardiola caved in'

'But behind the scenes, he was always pressing and making demands. In the end, Guardiola caved in and Zlatan lost out.'

At Old Trafford this Saturday, Guardiola will be without his own primary centre forward Sergio Aguero, absent through suspension. Ibrahimovic, meanwhile, will play on the back of three goals in his first three Premier League appearances.

Now 34, Ibrahimovic will not lack motivation. As he wrote in his book: 'Hatred and revenge get me going.'

Ibrahimovic will be hoping to inflict a defeat on his old manager Guardiola on Saturday

Manchester City chief executive Ferran Soriano, once of Barcelona, said of Jose Mourinho: 'What doesn't change is his methods. He wins and then off he goes.'

That is not as unfamiliar to Soriano as it may be to some at Manchester United. In Spain, coaches have always worked in relatively small cycles.

United have actually hired Mourinho in similar circumstances to Real Madrid in 2010. Six years ago, Real were desperate to make up ground lost to Barcelona and hired Mourinho with risks attached. This summer, United did likewise on the back of three fallow post-Ferguson years.

Guardiola's challenge is simply to hold back the forthcoming tide, on and off the field.

Manchester United have appointed Mourinho in similar circumstances to Real Madrid in 2010

Now 45, the City manager has hard edges of his own. He has changed some things at City. Some good staff have left the club — not just goalkeeper Joe Hart — while some of the club's junior coaches have commented privately that training sessions are now visible to invited personnel only.

Guardiola and Mourinho have already met since arriving in Manchester this summer. Both attended a Premier League managers' meeting in Stoke last month and, according to those present, there were handshakes and basic pleasantries.

But some who know him say that Guardiola changes physically at the mention of Mourinho's name.

His biographer Guillem Balague writes: 'An invisible wall pops up. His neck muscles tense, his shoulders hunch and he stops looking you in the eye.'

Guardiola admitted that his arduous battle with Mourinho eventually took its toll

By Guardiola's own admission, his 24 months in opposition to Mourinho in Spain wearied him. 'With Mourinho, so many things happened,' he has said reflectively. 'So many things.'

Here in England, the City manager knows at least that the Mourinho effect will be diluted by the presence of other leading adversaries. In Spain only two men mattered. In England, there is Arsene Wenger's Arsenal, Jurgen Klopp at Liverpool and, of course, the presence of Mourinho's beloved Chelsea.

If Mourinho obsesses with Guardiola like he undoubtedly did between 2010 and 2012 then other teams will fly past. Meanwhile, for all that the Portuguese may suggest otherwise, the days of mutual appreciation between two men who once shared something fundamental have long gone.