The Begining

The present teams and coaches.

As usual politics and it's extra long roots creep in everywhere, even these mighty clubs have long been politically motivated. As early as 1930's the two clubs started to be in tune with two opposing political traditions, FCB for Catalan pride and tradition and RM for centralizing tendencies of Madrid.
During the Franco dictatorship, most citizens of Barcelona were in strong opposition to the fascist-like régime. Phil Ball, the author of Morbo: The Story of Spanish Football, calls the El Clásico "a re-enactment of the Spanish Civil War". A similar analogy was made by American author Robert Coover, which described the 1977 match between the "archrivals" Barcelona FC and Real Club Deportivo Español as "more like a reenactment of the Spanish Civil War than a mere athletic event."
The first match between them was held in 1902 but the first match between them whose score i could find is the match in 1929 February 17, in which RM won 2-1.
And from then on The Fight was on.