The other is currently the outstanding central midfielder of his generation and a hero to thousands of Celtic and Scotland supporters.
Concerns may have been expressed about whether John Collins will be able to work with Scott Brown at Parkhead.
They were certainly issues between the two men during their time together at Hibs which culminated in the now infamous meeeing at the home of then-chief executive Rod Petrie.
The Easter Road players, who were unhappy with training methods and team selection, may have made a public apology shortly after that.
The fact that Collins, who had led them to the League Cup in 2007, departed later that year led to insinuations that the rift was never properly healed.
But the similarities between the two men, on the field of play at least, are uncanny.
And both have declared, privately and publicly, there is no bad blood.
Yes, they are different personalities, and then some, off the pitch.
Brown is invariably at the centre of any practical jokes or carry on in the dressing room. Collins is a far more cerebral and sophisticated character.
Each individual, though, is confident they can work alongside each other now and help Celtic achieve success both domestically and in Europe.
Brown was contacted by new manager Ronny Deila when the possibility of appointing Collins as his assistant was first mooted to see if it would be a problem.
The Celtic captain assured the Norwegian coach there was no lingering antagonism between them and he had no difficulty with the appointment.
And Collins, too, has dismissed suggestions that there may be friction between them when the players meet up for pre-season training at Lennoxtown next week.
The last thing Deila needs is for there to be any disharmony in the camp before a ball has been kicked in earnest and his new No.2 has poured cold water on any suggestion there will be a problem.
"Scott is a fantastic professional and an excellent player and I am looking forward to meeting up with him and working with him again," said Collins.
"When Gordon Strachan was the Celtic manager he asked me about Scott when he was thinking about signing him. I had no hesitations in recommending that he make a move for him.
"It has turned out to be a good recommendation as he has done very well. He is the captain of the club and plays well every week as well as internationally.
"I always got on very well with Scott on the training pitch at Hibs. I never had any problems with him whatsoever.
"He loves to work hard and play well and he did that for me at Hibs week in, week out. That is why he has done so well in his career."
The bust-up between the squad and the manager at Hibs all those years ago was downright bizarre - as was its fallout.
Indeed, the interview with Brown in the first game after the meeting with Petrie became public knowledge is now something of a YouTube classic.
So it is inevitable that Collins, who has since managed Charleroi in Belgium and been director of football at Livingston, was asked about it.
BUT the relationship that is of a far greater importance to Celtic is the one that the Scot forges with the manager in the months ahead.
Deila spoke in glowing terms about the qualities that his new No.2 will bring to his role earlier on this week.
Collins, despite the time he has spent as a manager in his own right, will have no problems acting as an understudy to a man who is eight years his junior.
They have spoken at length in person on two occasions since the former Everton, Fulham and Monaco player's name was raised.
Collins said: "Hopefully I can do my bit to help the players enjoy success on the park. Hopefully I can help to improve them as players and improve the team.
"I would like to think that I can bring some knowledge to this role and help out on the training pitch.
"I know what it is like to play for Celtic. I know the demands there are on the players here to win games and trophies and be successful.
"I will be there to offer an opinion if the manager wants to ask me, but ultimately the big decisions and the team selection will be down to him.
"But I will still be working hard and help out in whatever way that I can. I am looking forward to what is a great challenge.
"I like to try and improve players by working with them on the training ground and by taking sessions that challenge and motivate them."
He continued: "Ronny and I had a long chat a couple of weeks ago and then we went for a long dinner and just talked football.
"I think that we share the same football philosophy and I think that is very important if you are to work together successfully.
"We will be straight into meaningful games with the Champions League qualifiers coming up in the middle of next month.
"We will have high pressure games to cope with and win very early on. But that is what happens when you are at a club like Celtic."