Rangers play Celtic on Sunday in the Old Firm derby. It's the most passionate local rivalry in football and their is absolutely no love lost between the two Glasgow giants.
There are a handful of players who have a unique perspective on the Old Firm clash, having played for both teams. Here are the five footballers who have played for Celtic and Rangers.
5. Alfie Conn
The first post-War player to play for both Old Firm sides was the winger Alfie Conn. Starting his career at Rangers, Conn was part of the team that won the European Cup Winners' Cup in 1972 and also played in Rangers' 3-2 Scottish Cup victory over Celtic in 1973, in which he scored his team's second goal.
Conn's performances attracted the interest of Tottenham, who paid a then large fee of £140,000 in 1974. He would spend three years at White Hart Lane, before Celtic came calling. Conn's desire to play for Jock Stein saw him make the move to Parkhead.
"He was one of those managers I always wanted to play under. Rangers hadn't come back in for me and I thought I could still learn a lot. So when Stein asked me, I didn't hesitate. Several people warned me against it but it was only after I signed when I flew back into Glasgow, with all the press and TV, that I realised it was bigger than I first thought. That's when it hit home. It wasn't easy hearing the team that used to cheer for me throwing insults but at least it kept the city talking."
4. Mo Johnstone
By far the most controversial instance of a player playing for both Celtic and Rangers came when Mo Johnstone was signed by the Ibrox boss Graeme Souness. Having joined Celtic in 1984, Johnstone was a prolific scorer for the club, until he was bought by Nantes in 1987.
After two years in France, Johnstone appeared at a press conference at Parkhead, with Celtic having reputedly agreed a £1.2m deal to bring the striker back to the club. At the time Johnstone was quoted as saying: "I didn't want to leave Celtic and I don't intend to now. There was some rubbish about me wanting to join Manchester United but it never entered my head to play for any other club. In fact, there is no other British club I could play for apart from Celtic."
Due to financial complexities the deal never went through and less than a month later Johnstone signed for Rangers, whose fans seemed even more appalled at the deal than those of Celtic, with many burning scarves and handing in season tickets.
3. Steven Pressley
Hailed as the 'new Richard Gough, Steven Pressley was a product of the Rangers youth system, but struggled to establish himself as a first team regular and eventually left the club in 1994, signing for Coventry.
After a short spell in England, Pressley returned to his homeland with Dundee United, before moving to Hearts, where he made over 300 appearances and became the club captain. After becoming a free agent, the then 33-year old Pressley was signed by Celtic. In 2007 'Elvis' was part of the Celtic side that won the Scottish Cup and became the first player to have won the trophy with three different clubs.
2. Mark Brown
Another Rangers youth product who eventually ended up at Celtic was the goalkeeper Mark Brown. He would make just five first team appearances for Rangers, before moving to Motherwell in 2001, where he spent a single season until their financial problems forced them to release Brown from his contract.
The keeper then moved to Inverness CT where he would spend five years. When his contract due to expire in 2007, Celtic swooped to sign Brown for an undisclosed 'six-figure fee', where he would serve as backup to Artur Boruc. As was the case at Rangers, Brown was unable to establish himself between the posts at Celtic and made just 13 appearances for the club, before signing for Hibs in 2010.
1. Kenny Miller
Of the five players who have played for either side of the Old Firm in the modern age, Kenny Miller is the only one to have crossed the divide twice. Signed by Rangers in 2000 for £2m, Miller spent just over a season at Ibrox before moving to Wolves on a loan move that turned permanent.
Miller would spend five years in England with Wolves. His contract expired in 2006, allowing Miller to make a controversial Bosman move to Celtic. After failing to score in his first nine games, his debut goal for the club inevitably came against Rangers. The striker never became at regular starter for Celtic and he was quickly sold to Derby.
In 2008 Miller made history when he was signed by Rangers for the second time. It was an unpopular move amongst a proportion of Rangers' support. Walter Smith spoke out against the fans that booed their own player: "If people don't think he's good enough then that's fine but it's my opinion that matters and I happen to think he is good enough.
"That's how I look upon it. Everyone is entitled to their opinion but if their reason for not liking him is because he used to play for Celtic, then I thought those days were in the past. They are for me."