Cologne - It is one of the fiercest rivalries in world football: Borussia Dortmund and FC Schalke 04. The Revierderby brings emotions to boiling point, but the clubs and their fans share a common identity, forged as they were in the foundries and furnaces of the Ruhr district - Germany’s industrial and footballing heartland.

It’s a region founded on hard-work, dedication and a deep sense of loyalty. Perhaps more than anywhere else in Germany, fans in the Ruhr district expect to see these values conveyed on the pitch. Commitment to the cause is indispensable if a player is to endear himself to the supporters.

Usually, that would be rendered impossible if a player were to join his team's biggest rivals. Yet, by adhering to the fundamental Ruhr principles, some players have managed to cross the tricky divide and find acceptance on the other side.

FC Schalke 04 meant everything to Stan Libuda, and Stan Libuda meant everything to the fans in Gelsenkirchen. The wing-wizard came up through the ranks at Schalke and terrorised opposing defences for the Royal Blues between 1961 and 1965. However, it was with Dortmund that he scored the most important goal of his career - the extra-time winner in the 1966 European Cup Winners’ Cup final as Borussia beat English Premier League giants Liverpool FC to become the first German side to lift a European trophy.

After making his Bundesliga debut for Borussia in 1984 at the tender age of 20, Anderbrügge established himself as a first-team regular over the next four seasons. Then, the highly-regarded attacking midfielder dropped the bombshell and moved to Gelsenkirchen. Over the next 11 years he helped the club to promotion in 1991 and cemented his place in Schalke folklore as one of the legendary “Euro-fighters” who lifted the UEFA Cup in 1997. His role in that campaign, coupled with 82 goals in 321 appearances, led to him being voted into Schalke’s 'team of the century'.

A key figure in Dortmund’s most successful era, winning two Bundesliga titles and the UEFA Champions League in the mid-1990s, Möller was a black-and-yellow icon. After his BVB contract expired at the end of the 1999/2000 season, his decision to join Schalke sent shockwaves through the Ruhr district. Dortmund fans were aghast at the apparent betrayal, whilst die Knappen were unwilling to welcome a player so synonymous with their rivals’ success. Yet in his first season, Möller was the driving force in a Schalke side that was only denied the title with the very last kick of the season.

Not one to balk at breaking boundaries, Freund was one of the first players from East Germany to move to the West following the fall of the Berlin Wall, joining Schalke from Stahl Brandenburg in 1991. After just two seasons in Gelsenkirchen, he crossed another ideological barrier and signed for BVB. In five trophy-laden years in Dortmund, Freund won the Bundesliga twice, the UEFA Champions League and was a member of the Germany squad that won the 1996 UEFA European Championship. He later enjoyed success as a coach with Germany's youth teams and as an assistant coach with Tottenham Hotspur FC.

A goal at the Westfalenstadion secured hero-status at Schalke for Jens Lehmann. In the last-minute of the Revierderby in December 1997, the Royal Blues were trailing 2-1 as Lehmann charged upfield for a corner... and promptly equalised, becoming the first goalkeeper in Bundesliga history to score from open play. Lehmann was also a UEFA Cup winner with Schalke in 1997. After a brief spell with AC Milan, he returned to the Ruhr district in 1999, but this time to join arch-rivals Dortmund, where his displays in goal proved to be a major factor in helping BVB to the 2001/02 title.