John Cunningham played for many clubs in Glasgow, including turning out for Celtic and Rangers. He also played for Manchester United, Aston Villa and Sheffield United among other clubs in his career.
After joining Rangers in 1892, Allan Martin went through several loan spells before joining Hibernian in 1893 and Celtic in 1895. He made 17 appearances in his one season with Celtic.
Tom Dunbar is one of only two players who have crossed the Old Firm twice in their careers, the other being Kenny Miller. He played for Celtic in 1890-91 and Rangers in 1891-92.
Alexander King joined Rangers in the 1894-95 season as a guest player and made just one appearance. He moved to Celtic in 1896 and scored 17 goals in 56 games in his four-year spell there.
After a single season with Celtic in 1901-02, George Livingstone moved to Liverpool and Manchester City before joining Rangers in 1906, where he played for three years and scored 20 goals in 47 games.
Goalkeeper Tom Sinclair arrived at Rangers in 1904 and featured for them for two seasons, making 46 appearances before joining Celtic on loan in 1906. He made just six appearances for them before moving to Newcastle United in 1907.
1905-06 Scottish Premiership winner, Hugh Shaw was at Rangers before arriving at Celtic.
Willie Kivlichan joined Rangers in 1905 from Glasgow University, where he was an undergraduate in the field of medicine. He made 20 appearances for them before joining Celtic in 1907. The striker made 77 appearances and scored 20 goals for Celtic.
Versatile defender David Taylor arrived at Rangers in 1906 and stayed at the club until 1910 before joining Bradford and Burnley, where he became a club legend. His last stint in his professional career came at Celtic, where he featured as a guest player.
Rangers signed Scott Duncan in 1913 after his impressive performances for Newcastle United. He made over 100 appearances for the Glasgow outfit, scoring 26 goals. He became a guest player for Celtic twice during the World War.
James Young played at Celtic on loan from Lochgelly United and made just one appearance in 1918. However, Celtic were unwilling to meet the £250 asking price for the player so he did not stay with the club and moved to Rangers.
After graduating from Rangers' academy, John Dowie joined Fulham in 1973. The midfielder then joined Celtic in 1977, making 14 appearances for them.
Like Dowie, Gordon Marshall graduated from Rangers' academy in 1982 before joining a host of other clubs until he arrived at Celtic in 1991. He made 101 appearances for the club.
After initially joining Rangers' academy, Craig Beattie transferred to Celtic's academy at a young age before featuring for their senior team 50 times between 2003 and 2007.
Sean Fitzharris enjoyed his youth career at both Rangers and Celtic but couldn't make a single senior appearance for either club.
Having previously joined Rangers' academy, Greig Spence arrived at Celtic's youth system in 2009 before making it to their senior team in 2011.
Another player from both clubs' youth academies, Joe Thomson made just one appearance for Celtic between 2015 and 2018.
Celtic signed Dylan McGeouch from Rangers' academy in 2011, and he made 20 appearances for their senior team between 2011 and 2015.
Gregg Wylde spent most of his youth career at Celtic before joining Rangers' academy in 2005. He was promoted to their senior team in 2009 and made 38 appearances.
Barry Robson was at Rangers' academy between 1995 and 1997. After impressive senior spells at clubs like Inverness Caledonian Thistle and Dundee United, he joined Celtic in 2008 and spent two seasons there.
Celtic youth academy product Michael O'Halloran joined Rangers in 2016 and spent two seasons there, making 29 appearances.
After three appearances in three years at Rangers, midfielder Liam Burt joined Celtic in 2019. However, he didn't make an appearance for them in his one-season spell.
Lewis Morgan was at Rangers' youth academy between 2004 and 2013 before joining St. Mirren in 2013. He went on to feature for Celtic between 2018 and 2020.
Rangers youth product Greg Taylor moved to Kilmarnock in 2016. The left-back made 111 appearances for them before joining Celtic in 2019.