Martin O’Neill is a Celtic legend, there is no doubt.
O’Neill is one of Celtic’s most successful managers of all time having won a domestic Treble in his first season in charge of the club.
All in all, the Northern Irishman lifted seven major honours as Hoops boss before leaving the Parkhead club in 2005.
Of course, his recruitment was a massive factor in his success and Celtic were able to provide O’Neill with significant funds to overhaul Rangers.
Chris Sutton, Neil Lennon and John Hartson were his most expensive purchases, with Belgian defender Joos Valgaeren coming up in fourth spot.

Ex-Celtic defender Joos Valgaeren now a sewer expert
Valgaeren was signed for £3.8m in 2000 and went on to make 178 appearances for the Bhoys across five years in Glasgow.
He played in the UEFA Cup final defeat to Porto in 2003, but now it’s been revealed by Valgaeren himself that he works as a sewer disconnection expert.
It’s a far cry from playing at the top end of European football with Celtic and winning multiple domestic honours.
As quoted in the Daily Record, Valgaeren has said: “After I quit football, I studied to get a diploma as a certified land surveyor and I got a job at a company responsible for water purification.
“It was a fantastic job that I did for 11 years, but I recently retrained as a sewer disconnection expert. We visit private individuals or organisations to see how we can improve their sewer systems.
“Going back to study was really hard at first because I hadn’t held a textbook in my hands for about 20 years.
“But those feelings soon disappeared and actually, I’m almost as proud of overcoming that hurdle as I am of my football career.”
Who else did Valgaeren play for?
Valgaeren was already an experienced campaigner when he joined Celtic in 2000, having played for K.F.C. Verbroedering Geel, KV Mechelen and Roda JC beforehand.
He earned 19 caps for Belgium between 1997 and 2003 as his displays for Roda JC propelled him into the national team sphere.
Valgaeren was actually linked with transfers to Ajax and Bayern Munich in 2000 after he won the Dutch Cup final.
But it was Celtic who convinced him to sign, before going on to form a formidable three-man defensive unit with Bobo Balde and Johan Mjallby.
After Celtic, Valgaeren played for Club Brugge for three years and then finished his professional career at FC Emmen in the Netherlands.
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