Controversies

A rivalry doesn't go without controversies. The El Clasico was from the very beginning were surrounded by controversies. The most popular among them is the "Di Stéfano transfer", Di Stéfano had impressed both Barcelona and Real Madrid whilst playing for Club Deportivo Los Millonarios in Bogota, during a players' strike in his native Argentina. Both Madrid and Barcelona attempted to sign him and, due to confusion that emerged from di Stéfano moving to Millonarios from River Plate following the strike, both clubs claimed to own his registration. After intervention from FIFA representative Muñoz Calero it was decided that both Barcelona and Real Madrid had to share the player in alternate seasons. Barcelona's Franco-imposed President backed down after a few appearances, as Barcelona's side claimed, but Real say Barcelona's decision was voluntary and di Stefano moved definitively to Madrid.

Di Stéfano became integral in the subsequent success achieved by Madrid, scoring twice in his first game against Barcelona. With him, Madrid won the initial five European Champions Cup competitions. The 1960s saw the rivalry reach the European stage when they met twice at the European Cup, Real Madrid winning in 1960 and FC Barcelona winning in 1961.

Recently

The two teams met again in the UEFA Champions League semi-final in 2002, with Real Madrid winning 0-2 in Barcelona and a 1-1 draw in Madrid. The match, dubbed by Spanish media as the Match of the Century, was watched by more than 500 million people. In the Clásico held on November 2005, Barcelona played away in Madrid, winning 3-0. The star of the Barcelona team was Ronaldinho, who became the second Barcelona player after Diego Maradona to receive a standing ovation from Real Madrid fans.

The rivalry has been strengthened throughout time by the internal transfer of players between the clubs. Barcelona players who have later played for Real Madrid includeBernd Schuster, who switched in 1988, Michael Laudrup went to Real Madrid on a free transfer in 1994, but the most notorious was former vice-captain Luís Figo's switch in 2000. Players transferring from Real Madrid to Barcelona are less frequent, the most recent being Luis Enrique, who went to Barcelona in 1996 where he went on to captain the Blaugrana, and since 2008, coaches the reserve team.

FANS

A 2007 survey by the Centro de Investigaciones Sociológicas determined that Real Madrid was the team with the largest following in Spain. Thirty-two percent of the Spanish population supported Real Madrid, while twenty-five percent supported Barcelona. In third place came Valencia CF, who were supported by five percent. Barcelona in turn is more popular in Europe than Madrid. According to a survey made by the German research agency Sport+Markt in 2010, Barcelona has approximately 57.8 million fans around Europe, while Real Madrid has 31.3 million fans. Globally, Real Madrid is the most popular football club in the world according to a study performed by Harvard University in 2007, with over 228 million supporters worldwide.
PS- I'm a fan of RM.