The 9 was achieved with 116 players over 334 matches. These are the men behind the 9.
One
There has to be a leader in the appearance list and that is captain Scott Brown. Not only did he appear in all 9 title campaigns, he leads on appearances with 256, 34 more than any other player and one of only two players over 200. Averaging over 28 appearances per title he never made less than 17 (2012/13). Brown should surely be considered a giant of this football club for all time.

Two
There were two men who played more than 200 times for Celtic across all 9 campaigns. Brown led the field in more ways than one, but after that comes one of our own. James Forrest has appeared in 222 matches averaging 24.7 appearances per title, and never appearing less than 15 times. Forrest has blossomed with age and in the last three campaigns has 96 appearances, 29 goals and 35 assists. He looks like being a one club Bhoy and only 1 player has had more Scoring Contributions (goals and assists) than his 116.

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Three
Modern football has many demands with many competitions and European rounds starting in July and lasting (hopefully) beyond the new year. Being “ever present” in the age of 60 plus game seasons and 25-30 men squads is very rare. There are only three occasions players have been ever present in the 9 campaigns, and oddly two of them occurred in the same season:
Player
Season Games Ambrose 2013/14 38 Brown 2013/14 38 McGregor 2019/20
30
Four
Two players appeared in 4 different seasons yet racked up less than 20 league appearances between them. O’Connell managed 7 appearances in his 4 campaigns but Filip Twardzik only 5.
Five
There are two players who made league appearances in 5 different seasons yet only made 40 appearances in total. Liam Henderson saw action 29 times across 5 seasons whilst Ralston only accrued 11 appearances across the same number of campaigns.
Seven
There are four players outside of Brown, Forrest and one player who appeared in eight campaigns (see below) who contributed to 7 titles. The magnificent 7 medal haul owners are:
Player Appearances Izaguirre 157 Griffiths 151 Bitton 137 Rogic 117
Eight
Only one player appeared in 8 campaigns out the 9 and therefore is third behind Brown and Forrest in total medal haul. This player is 4th in the appearance list on 159 and who had 4 injury hit seasons amassing only 47 between 2011/12 and 2014/15. There then followed 4 golden seasons of 112 appearances before finally leaving us with a big gap in the right back position. That is of course – Lustig!

Eleven
A starting XI worth of players that managed just 1 appearance as their contribution to the 9. For this economy of effort, we salute you! In line up order (Bailly guests as the ‘keeper – 3 appearances):

Special mention to Arzani who lasted 23 minutes before being carried off with a cruciate injury but waved cheerfully enough from the stretcher – already a Celtic hero.
Twelve
There are 12 players who having played in at least 10 matches and average a goal or an assist every other game. These are the players with the best strike rates for goals and assist per appearance.

If I had the time I’d go back and work out all the minutes played which would be the best measure. But for now, based on total appearances, Hooper just edges Edouard as the most productive attacking player. They are joined by Moussa Dembele in that elite group averaging over 0.8 goals and assists per appearance. It is good news 4 of the 12 are still at the club.
Seventeen
There are 17 players who contributed in at least 100 games out of the 334 it has taken to win the 9. In order they are:
Player Appearances Seasons (at least 1 App) Brown 256 9 Forrest 222 9 McGregor 177 6 Lustig 159 8 Izaguirre 157 7 Griffiths 151 7 Gordon 147 5 Bitton 137 7 Commons 135 5 Forster 132 4 Rogic 117 7 Ambrose 113 4 Mulgrew 110 5 Stokes 106 5 Sinclair 104 4 Tierney 102 5 Matthews 101 4
Special mention to Armstrong on 98 who just missed out. McGregor has only made appearances in 6 of the 9 seasons yet has the 3rd most total appearances, a testament to his consistency. The goalkeepers Gordon and Forster benefit from relatively low injury and consistency of selection. Ambrose never missed a game injured for Celtic so even though he only appeared in 4 of the 9, he makes the list. But this list represents the spine of what took Celtic to all those titles. They were the constants and delivered season on season. Only 3 players (Brown, Forrest and McGregor) appeared in over 50% of all the games.
Twenty-Two
There are 73 different players that have provided assists for the 800 goals scored by Celtic in 9 league campaigns The top 22 have all managed more than 10:

Sixty-Two
As with goals scored, the champion assister is not a close competition. With 62 assists over 9 campaigns Forrest is the leader by 12 over Commons. Commons is also 3rd on the goal scorers list and his contribution to the 9 cannot therefore be undervalued. But the recent form of Forrest with 28 assists in the last two campaigns is hard to resist.

Sixty-Three
63 players have contributed to 785 goals (with 15 being own goals). The full list of scorers with more than 10 is:

Sixty-Four
The outfield player who made the most league appearances without scoring is Kayal, with 64.
Eighty-Four
The top scorer across the 9 is not a close competition. A player who has not had his troubles to seek appeared in 7 of the 9 seasons and is averaging over 10 per campaign. Griffiths is 30 goals ahead of the next challenger, Forrest, and stands alone as the single biggest contributor to the goal tally. He contributed 10.5% of all Celtic goals in this era!

One-Hundred and Sixteen
Here it is – the list of all the players, all 116, who have played even a minute in bringing home the 9. As fans, we’d all settle for just that minute. See how many you had forgotten!
Apps Brown 256 Forrest 222 McGregor 177 Lustig 159 Izaguirre 157 Griffiths 151 Gordon 147 Bitton 137 Commons 135 Forster 132 Rogic 117 Ambrose 113 Mulgrew 110 Stokes 106 Sinclair 104 Tierney 102 Matthews 101 Armstrong 98 Boyata 90 Edouard 81 Ajer 80 Ledley 77 Van Dijk 76 Simunovic 75 Johansen 73 Ntcham 72 Samaras 71 Hooper 68 Kayal 64 Wanyama 61 Christie 57 M. Dembele 55 Roberts 55 K. Wilson 47 Mackay-Steven 46 Hayes 45 Sviatchenko 42 Bain 29 Denayer 29 Johnston 29 Ki 29 L. Henderson 29 Jullien 28 McCourt 28 Rogne 27 Pukki 26 Watt 25 Guidetti 24 Balde 20 Benkovic 20 Gamboa 20 McGeouch 20 Scepovic 18 Fisher 17 Majstorovic 17 Boerrigter 16 Hendry 15 Zaluska 15 Bolingoli 14 Burke 14 Cha 14 Frimpong 14 Lassad 14 Morgan 14 Allan 13 Weah 13 Ciftci 12 Janko 12 Kouassi 12 Taylor 12 Bangura 11 Kazim-Richards 11 Loovens 11 Miku 11 Ralston 11 De Vries 10 Elyounoussi 10 Bauer 9 Bayo 9 Toljan 9 Toure 9 M. Wilson 7 O'Connell 7 E. Henderson 6 El Khaddouri 6 Tonev 6 F. Twardzik 5 Wakaso 5 Atajic 4 Berget 4 Cole 4 Elhamed 4 Miller 4 Musonda 4 Aitchison 3 Bailly 3 Blackett 3 Browek 3 Gershon 3 Maloney 3 Chalmers 2 Herron 2 K. Dembele 2 Klimala 2 Mouyokolo 2 Arzani 1 Benyu 1 Fraser 1 Irvine 1 Mulumbu 1 Murphy 1 Rabiu Ibrahim 1 Shved 1 Slane 1 Thomson 1 Welsh 1
One Hundred and Seventeen
Only 3 players have contributed more than 100 Scoring Contributions (goals and assists) to the 9 in a row league seasons.

It’s a close call but Griffiths just edges Forrest by volume and on average per appearance. 117 goals contributed to out of 800 scored means Griffiths has been directly involved in 15% of Celtic’s 9 in a row goals.

Eight Hundred
Celtic have scored exactly 800 goals in their 9 winning seasons, 88.88 per season, fittingly. 63 different players have scored, with Mr. Own Goal, our old friend, chipping in with 15. 23 players have managed 10 or more, whilst 11 scored only 1 league goal. Those whose historical legacy to 9 is a solitary goal?
Aitchison Atajic Boerrigter Cha El Khaddouri Gershon Kazim-Richards Loovens Ralston Rogne Sviatchenko
Legends every one!
Conclusion
What is telling is that runs such as this are not solely founded on the best players. At a club in Celtic’s position, the Van Dijk’s, Dembele’s, Wanyama’s do not stay for 9 years any more. No, the men behind the 9, those that were here for 6, 7, 8, 9 seasons are back bone players. Good performers, consistent, the 7 out of 10-ers. Players you build your team round who likely would never play at a bigger club than Celtic but nevertheless perform season after season. This isn’t to damn with faint praise or to patronise, but the likes of Brown, Forrest, Commons, Lustig, Izaguirre, Griffiths, Gordon, Bitton would not be in most people’s top 10 players of all time, but they and others have made a massive contribution to this era of dominance. Keeping a core of similar players together, supplemented with bright sparkling talent that will shine for a season or two, is the way to go for Celtic as they embark on the next 9.