At any level of football, rivalries and derby matches are always among the most eagerly anticipated fixtures on the calendar. These intense games can bring the best out of managers, players and supporters to produce truly memorable occasions.
Equally, some great rivalries are not those rooted in history between teams, but in the personal battles - both on and off the football pitch - between individuals. These public feuds can add an extra dimension to an already enthralling contest.
Here are six of the greatest rivalries in football history.
Lionel Messi vs Cristiano Ronaldo
When it comes to domestic football, the 21st century belongs to Lionel Messi and Cristiano Ronaldo, and the nine years when they faced each other in La Liga will go down as one of the golden periods in sporting history. Ronaldo may have left for Italy now, but the debate about who is better will rage long after they have both retired.
Between them, they have scored 1155 club goals in competitive matches, winning nine Champions League trophies and 14 league titles. The last ten Ballons d'Or have been divided evenly between the two men, as have eight of the last ten European Golden Shoes.
Their rivalry has been an honour to witness, and long may it continue.
Celtic vs Rangers
Scotland may not be able to compete with their neighbours when it comes to money or quality, but the Old Firm derby between Celtic and Rangers is the most intense rivalry in Britain and one of the most divisive derbies in world football, with the divisions drawn down political lines as well as footballing ones.
Every Scottish title since 1985 has been won by one of the two Glasgow clubs, although Celtic have dominated in recent years after Rangers were demoted to the fourth tier in 2012.
The Gers are nearing the time when they can be competitive again, and all neutrals will rejoice - Scottish football needs a strong Celtic and a strong Rangers.
Sir Alex Ferguson vs Arsene Wenger
Sir Alex Ferguson and Arsene Wenger both defied the usual managerial life expectancy by serving for over 20 years each as managers of Manchester United and Arsenal respectively. For nine consecutive years between 1996 and 2004, Ferguson and Wenger held a duopoly over the Premier League title as a fierce rivalry developed between their teams.
Unlike Messi vs Ronaldo, there was an undisputed winner in this contest. Ferguson bowed out in style after winning his 13th Premier League in 2013, while Wenger remained stuck on three titles and his departure earlier this year was well overdue.
Both belong in the pantheon of greats though, and their longevity is unlikely to ever be repeated.
Argentina vs Brazil
Argentina and Brazil haven't met at a World Cup since 1990 and neither side has won the tournament since 2002, yet the rivalry remains as fierce as ever. Argentina could have inflicted the ultimate insult by winning the World Cup on Brazilian soil in 2014, but they lost in the final to Germany - much to the relief of all Brazilians!
Both countries also lay claim to having produced the best footballer of all-time: Brazilians believe Pele is the GOAT, while Argentineans favour Lionel Messi or Diego Maradona.
Both nations flattered to deceive at this year's World Cup, but here's hoping they can soon produce teams worthy of their historic rivalry.
Pep Guardiola vs Jose Mourinho
Pep Guardiola and Jose Mourinho first locked horns as managers of Barcelona and Inter, who met in a famously tempestuous Champions League semi final in 2010. Their rivalry became a regular occurrence when Mourinho took over at Real Madrid later that year, and their head-to-head has now made the move to Manchester.
Barbs have flown back and forth throughout their rivalry, with Mourinho implying in 2011 that Guardiola's Barcelona owed their success to many incorrect referee decisions. Guardiola has criticised Mourinho's 'results over spectacle' approach to management; Mourinho later made the bizarre claim that Guardiola's baldness is a sign he doesn't enjoy football.
Guardiola has generally had the upper hand against Mourinho, winning twice as many matches between the pair as his Portuguese counterpart. Mourinho would love nothing more than to knock Guardiola and Manchester City off their perch, though it seems unlikely at the moment.
Barcelona vs Real Madrid
Spanish football's biggest fixture has borne witness to many of football's great rivalries of the modern era, whether it be Messi vs Ronaldo, Guardiola vs Mourinho, or Gerard Pique vs Sergio Ramos.
But El Clásico transcends all of those, remaining the most eagerly anticipated derby in European football regardless of who is involved.
This rivalry has only grown in intensity over recent years as the two sides have maintained a fierce stranglehold over European and Spanish football, with one or the other winning seven of the last ten Champions Leagues (including the last five) and 13 of the last 14 La Liga titles.
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