Both clubs are among the most decorated sides of all time and are two of the most followed and financially successful sides in football. They, therefore, have had the clout and muscle to attract some of the world's best players throughout history.
A list of past players to have graced El Clasico reads like a who's who of footballing royalty and with 23 Ballon d'Or winners between them, Barcelona and Real Madrid thump all the others in terms of personal accolades.
However, one name that stands heads and shoulders above the rest is that of Cristiano Ronaldo who, for nine seasons, made a legendary mark on the fixture.
The former Manchester United man made 30 appearances for Real Madrid against Barcelona, scoring 18 goals and assisting once and his impact on the history of Los Merengues cannot be overlooked.
His record-breaking transfer to Juventus in the summer of 2018 ended his Clasico legacy and in many ways, the fixture lost some of its essence when the five-time Ballon d'Or winner exited the scene.
In this piece, we shall be highlighting three reasons why El Clasico has not been the same since Cristiano Ronaldo departed Real Madrid.
#3 His showdown with Lionel Messi was a key subplot in the game
Cristiano Ronaldo and Lionel Messi are two of the most famous faces on the planet and with their status as two all-time greats guaranteed, football fans of this generation were extremely blessed to have witnessed their legacies from start to finish.
In many ways, their rivalry helped redefine the game and while there were muted comparisons between the pair at the early stage of their careers, Ronaldo's world-record transfer to the Bernabeu brought the two men in a head-on collision in Spain.
The two best players playing for the two best clubs in the same country at the same time, you would be hard-pressed to find a better-written plot in the history of football and fans were the better off for this.
Owing to the massive fanbases of the two superstars, discussions and sometimes fatal debates have arisen over who the better player is and while it might be virtually impossible to determine or convince the other party, for nine years, both sets of fans saw El Clasico as an opportunity for their player to silence the opposing group.
There were at least two LaLiga clashes involving Real Madrid and Barcelona every season, while the Champions League, Copa del Rey, and Spanish Super Cup also offered a chance for the two greats to battle it out for 90 minutes and this was a marketing cash cow that benefited the federation hosting games between the iconic pair.
In what was perhaps an act of fate, Messi suffered an injury soon after Ronaldo's departure from Spain, with the result being that the 5-1 demolition suffered by Real Madrid in October 2018 was the first El Clasico in over a decade to feature neither of the two men.
Ronaldo and Messi have given us a beautiful story that might be unmatched anywhere in professional sports and El Clasico was a better spectacle for it. The Madeira native is the only player who can operate on the same level as his Rosario rival and his departure has left Messi playing god among mortals, with the world's biggest club game undoubtedly worse off for it.
#2 Real Madrid lost their chief source of goals
With 450 goals from just 438 matches, Cristiano Ronaldo is the greatest goalscorer in the history of Real Madrid, while his 131 assists are also more than anyone else has managed at the club.
Furthermore, his 18 goals are the joint-second highest tally in the history of El Clasico (behind Messi on 26) and also the joint-highest for Real Madrid (alongside the legendary Alfredo di Stefano) and with Karim Benzema further behind on nine goals, it would be a while before any Los Blancos player usurps him.
It is no hidden secret that Real Madrid have struggled for goals since Ronaldo's departure, with their subpar performance last season indicative of this and while Benzema might have started the season brightly, he has endured a poor run of form this year, scoring just two goals from his last 13 matches.
Nowhere is their paucity of goals more evident than in El Clasico, where the bluntness of the Los Blancos attack has been brutally exposed by the Blaugrana. In five matches against Barcelona since Ronaldo departed, Real Madrid have scored just two goals, while they have conceded 10 and it is hard to imagine them being on such a poor run if their record goalscorer was still within the ranks.
#1 His otherwordly ability saw him decide matches almost single-handedly
Following the arrival of Pep Guardiola as Barcelona manager in the summer of 2008, the club transformed on a scale never seen before and went on to conquer all and sundry on their way to becoming arguably the best club team in football history.
In many ways, their 6-2 victory over Real Madrid at the Santiago Bernabeu in May 2009 was a statement of intent and sent shockwaves in the Spanish capital, leading to radical changes including the return of Florentino Perez as club president, the ushering in of the second Galactico era, and the appointment of Jose Mourinho as manager.
Real Madrid pushed Barcelona but the difference was still clear and while the capital side might have flexed their muscle on the continent, the domestic bragging rights belonged to the Catalans and the Blaugrana had the advantage in Clasico meetings.
Their dominance has been exacerbated since Ronaldo departed, with Real having failed to win any of the five fixtures against Barcelona since then. This is not in any way to suggest that Real Madrid were invincible against Barca when they had Ronaldo and his record of eight wins, eight draws, and 14 losses from 30 El Clasico fixtures paints a better story of just how one-sided the games have been in the last decade.
However, the Portuguese superstar is an otherworldly talent who can make a difference in the twinkling of an eye. Throughout his career, the 35-year-old has shown a penchant for almost single-handedly deciding games on his own and most of his 18 goals against Barcelona came in iconic moments that left a lasting impact.
There was the thumping header in extra-time during the final of the 2011 Copa del Rey in Valencia that proved to be the difference between Real Madrid winning a first cup title in almost two decades and Barcelona winning their second treble in as many years.
His late strike in the 2-1 win at Camp Nou in April 2012 also ended Barcelona's run of three consecutive league titles, 55 matches unbeaten at home in all competitions, and eight league matches undefeated against Madrid, kickstarting a disastrous week that saw them eliminated from the Champions League by Chelsea in what was the beginning of the end of the Guardiola era.
Even though the Blaugrana's superiority meant that they got the better of Los Blancos on most occasions, the presence of Ronaldo was an X-factor that always put their defence on high alert but in his absence, the Blaugrana could well dominate their biggest rivals for the foreseeable future.