We continue our countdown of the greatest 30 players to wear the famous green-and-white.
Just ahead of European Cup final hero Stevie Chalmers at number 27 in our countdown of the greatest 30 footballers to play for Celtic is a man who became one of Martin O'Neill's first signings at Parkhead.
Bought from Aston Villa for £2.75 million in 2000, Alan Thompson was a relative unknown quantity at the time of his move after an injury-plagued two years at Villa Park.
After an inauspicious start to his debut season at the club, in which he was sent off in a 5-1 defeat to Rangers at Ibrox, he won fans over later that campaign by scoring the only goal of the game against the club's Old Firm rivals at Parkhead.
Scoring in clashes against the Gers was a happy habit he developed in his six-and-a-half years in Glasgow, netting seven times against the Hoops' arch-rivals in total.
However, it was in European football that he perhaps enjoyed his best success for the club, something which started with him being an integral part of the side which reached the 2003 UEFA Cup final, with Thompson scoring a free kick in the quarter-final victory over Liverpool at Anfield.
His crowning moment came when he scored the only goal of the two-legged tie against Barcelona in the same competitions the following year as Celtic achieved a famous win over the Spanish giants.
Often overshadowed by such contemporaries as Henrik Larsson and Chris Sutton, Thompson was nonetheless another of the players who typified O'Neill's reign, and it was perhaps fitting that it was he who scored the winning goal to seal the Irish manager's last trophy at the club, the Scottish Cup in 2005.
The midfielder also became the first man to win an England cap whilst playing for Celtic at the time when he was given his only international appearance by Sven Goran Eriksson in 2004.
In total, Thompson scored 51 goals, many of them spectacular, in his 227 appearances for the club before leaving for Leeds United in January 2007.