Whether you're a diehard Scottish football fan, or have never watched a match in your life, everyone the world over knows that the Old Firm is one of the fiercest rivalries anywhere on the planet. Since first clashing in 1888, Celtic and Rangers have met over 450 times, winning 240 major trophies between them.
Thus, crossing the divide is extremely rare. In fact, since World War II, just five men have represented both the Hoops and the Gers at senior level. So, we will take you through all five, outlining how each achieved this rare and controversial feat.
1) Kenny Miller
The most recent and famous player to play for both of Glasgow's big two in modern times is undoubtably Kenny Miller. The striker racked up 300 appearances and 115 goals across three spells at Rangers. He returned to the club when they were still in the Championship, helped them regain their place in the top-flight following liquidation.
No one would argue that Miller is a Rangers legend, making it bizarre that he had a season at Celtic. He spent just a year at Parkhead, scoring 11 times, before being sold to Derby Country. This, for some reason, has not tarnished his reputation across the city, and seems to be forgotten about.
Years at Celtic: 2006/07.
Years at Rangers: 2000/01, 2008-2011& 2014-2018.
Notable achievements: 4 Premiership titles, 2 Scottish Cups & 1 League Cup.
2) Mo Johnston
The most infamous example of any player crossing the Old Firm divide in history has to be Mo Johnston. The forward spent three seasons at Celtic, before departing for France in 1987, signing for Nantes. However, after two years at Stade de la Beaujoire, he did the unthinkable.
Ally McCoist recounts that, while away on international duty, his close friend Johnston told him that he was going to be joining Rangers. Shocked, McCoist told him that he must be insane, but Johnston did become, officially, the first Catholic to ever be employed by Rangers in any role. He would go on to be a key figure in the success enjoyed under Graeme Souness, including being the club's top-scorer in 1990/91, before departing to join Everton the summer.
Years at Celtic: 1984-1987.
Years at Rangers: 1989-1991.
Notable achievements: 3 Premier Division titles & 1 Scottish Cup.
3) Alfie Conn
The very first post-war player to appear for both Rangers and Celtic is Alfie Conn junior. After beginning his career at Rangers in the late-60s, he joined Bill Nicholson Tottenham Hotspur and, despite a mixed spell in North London, was known affectionately as the King of White Hart Lane.
Thus, it was very controversial when he returned to Scotland to join Celtic, part of the 1977 Scottish Cup winning side against his former employers. Despite this, he was inducted into the Rangers hall of fame many years later, having played a key role in their Cup Winners' Cup triumph, starting the final win over Dynamo Moscow at camp Nou.
Years at Celtic: 1977-1979.
Years at Rangers: 1968-1974.
Notable achievements: UEFA Cup Winners' Cup title & 2 Scottish Cups.
4) Steven Pressley
Known now as the eccentric Dundee manager, Steven Pressley was once a very sold centre-back, representing Scotland 32 times in the early-2000s. During his club career, the man known as Elvis played for seven different clubs, starting out with Rangers.
After much longer stints at Dundee United and Hearts, he joined Gordon Strachan's Celtic in 2006, an experienced 33 years old by then. Pressley played just 23 times in hoops, including starting two Champions League matches, as well as the 2007 Scottish Cup final win over Dunfermline Athletic. Such is his close association with Hearts, especially during the infamous Vladimir Romanov years, it is often forgotten that Pressley did cross the Glasgow divide.
Years at Celtic: 2006-2008.
Years at Rangers: 1990-1994.
Notable achievements: 3 Premier Division titles & 2 Scottish Cups.
5) Mark Brown
Last, and perhaps least, Mark Brown was something of a journeyman goalkeeper. He had spells at Motherwell, Inverness Caledonian Thistle, Kilmarnock, Hibernian, Ross County and Dumbarton, racking up 385 senior appearances, which does include short stints at both Ibrox and Celtic Park.
He began his senior career on the west side of Glasgow, appearing just four times for the Gers, primarily standing in for Stefan Klos during Dick Advocaat's spell in charge in 2000. Seven years later, he joined Celtic to be Artur Boruc's understudy.
Brown did appear 15 times for the Celts, keeping seven clean sheets, most notably starting the first leg of a crucial Champions League play off against Spartak Moscow at the Luzhniki Stadium. He did not play an enormous role for Strachan's team, but did complete the rare feat.
Years at Celtic: 2007-2009.
Years at Rangers: 1999-2001.
Notable achievements: 2 Premiership titles & 1 League Cup.
In total, throughout history, just 20 men have made a senior appearance for both Celtic and Rangers, the vast majority of which did so before World War 1. Will we ever see a new name appear on this list? It does feel unlikely, but not impossible.
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