The French winger played for the club between 2000 and 2006, winning three league titles, three Scottish Cups and a League Cup.
For the majority of that time, he played under Martin O’Neill in one of the best periods in history for the club, before going on to make little to no impression under replacement gaffer Gordon Strachan.
And that led him to leave the club in 2006, joining O’Neill again at Aston Villa.
Agathe has been in the news today after an interview he did with sofoot.com, where he recalls his successful time at Celtic.
Speaking about O’Neill and Strachan, Agathe chose the signing of right back Telfer in 2005 to show how bad a manager the former Scotland boss is. Telfer is rumoured to be married to one of Strachan’s daughters.
Agathe, per sofoot.com, said: “I learned a great deal from Martin O’Neill from the personal point of view. He was a proper manager, he spoke with his players and fostered a real team spirit.
“However Gordon Strachan was totally the opposite. He brought in a right-back, Paul Telfer – and the guy was married to his daughter! There you go.
“I clashed with Strachan in my very first training session with him, as I was injured and he told me to train against the advice of the physios.
“He was hung up in comparison to O’Neill. I honestly didn’t learn a thing from him, and I’m not just saying this as I didn’t get to play.
“Gordon is truly everything that football should not produce.
“You get the impression that he is there because of his ego, and not because he wanted to pass on any knowledge.”
Agathe made 183 appearances for Celtic during his career, four of which came under Strachan during a transition period at the club after O’Neill’s exit.
He’ll always be remembered fondly by supporters for what he contributed to the club, as will Strachan, who went on to win three league titles, two League Cups and a Scottish Cups while manager.