The intense rivalry between Celtic and Rangers is widely considered to be the fiercest in world football by many supporters not just in Scotland but from all corners of the globe.
There have been over 400 contested derbies in history between the two Glasgow giants, with just over 100 games ending in draws. Throw in multiple instances of fan clashes and vast changes to stadium ticket allocations, matches between Celtic and Rangers rarely pass without incident.
Throughout the years there have been only a handful of players who have either represented or been on the books at one point for both clubs. Even fewer have played for both in the Old Firm derby or their modern name, the 'Glasgow derby' and no player has ever transferred directly from one club to the other.
Here, GlasgowWorld profiles 15 players who have either played for or been on the books at both Celtic and Rangers in the past 40 years and how they fared at each club:
1. Mo Johnston - Celtic 1984-1987. Rangers 1989-1991
Scotland international arrived at Parkhead in 1984 and scored an incredible 52 goals in just 99 appearances. Rangers boss Graeme Souness persuaded him to join Rangers in 1989 instead of heading back to the Hoops. He spent two seasons at Ibrox, winning two league titles.
2. Steven Pressley - Rangers 1990-1994. Celtic 2006-2008
Centre-back began his senior career within the Gers academy in 1990, making 34 first-team appearances before moving down south four years later. Had spells at Dundee United and Hearts before heading to Celtic in 2006 where he played only 19 times. Won a league title with both Glasgow clubs.
3. Kenny Miller - Rangers: 2000-2001, 2008-2011 & 2014-2018. Celtic: 2006-2006
Prolific striker had spells at both clubs sandwiched between his five-year spell at Wolves. Joined Rangers initially in 2000 and later spent a season at Celtic, netting seven goals in 33 games. It was under Walter Smith at Rangers where he thrived most, between 2008 and 2011, scoring an impressive 49 times in 81 matches. Returned to Ibrox for a third stint which also yielded an impressive goals tally.
4. Mark Brown - Rangers: 1997–2001. Celtic: 2007–2010
Goalkeeper made just four senior appearances for Rangers at the start of his career. Turned out for Motherwell, Inverness and Hibs and headed to Parkhead in 2007 under Gordon Strachan, joining as their back-up shot-stopper. He made 13 starts in three years.