Why Ronny Deila's Celtic contribution cannot be forgotten - Tony Haggerty

The affable Norwegian landed Scottish Premiership titles four and five for the Hoops en route to the club's second nine-in-a-row.

The former Stromsgodset boss had guided the unfashionable club to their first Norwegian title in 43 years before being asked to succeed Neil Lennon in the Parkhead hotseat.

The then 38-year-old was far from the finished article - he was, to all intents and purposes, a managerial work-in-progress.

Yet it's fair to say that Deila played a major part in Celtic’s modern-day success even if the overall experiment or project - call it what you will - was deemed a failure.

While his reign ultimately ended in disappointment it would be churlish to forget that there was a touch of the free-scoring, rip-roaring, never-boring Glasgow Celtic about Deila's charges towards the end of his first season.

Lest we forget in his debut campaign Deila was also competing in a league without the likes of Rangers, Hearts and Hibernian.

The Ibrox team were still making their way up the divisions while Hibs had somehow managed to get themselves relegated in a season where capital city rivals Hearts had been deducted 15 points at the very outset for entering administration.

Deila just had to steer the good ship Celtic and there was a whiff of treble talk in the air. Nobody could have - or should have really - stopped the Hoops from achieving total domestic dominance.

Disaster struck early in his Celtic tenure as the club were crushed 6-1 by Polish outfit Legia Warsaw on aggregate in the Champions League qualifiers. 

A shock but welcome reprieve arrived in the shape of Legia's rule break after they fielded an ineligible player. The Hoops advanced to face Slovenians Maribor in the final qualifying round ahead of the lucrative group stages.

Deila and the men from Glasgow's East End blew it big style at home by succumbing 1-0 to exit again on a 2-1 aggregate. The Europa League awaited, much to the support's chagrin.

The league, though, was surely a formality?

Josh Meekings' handball in the 2015 Scottish Cup semi-final

Their inauspicious start had alarm bells ringing, especially as the presumed domestic dominance seemed to be faltering too. League defeats to Caley Thistle and Hamilton in the first eight matches set a dismal tone.

Apathy set in among the supporters and the top tier of the stadium was shut. The team's play was poor and many players simply didn't seem to be buying what the manager was selling.

It wasn't all doom and gloom though. Deila managed to cobble together a fine defensive unit in the shape of inherited centre-back Virgil van Dijk and Manchester City loanee Jason Denayer.

The Duchman and the Belgian formed a formidable partnership with the loss of only 17 league goals which culminated in Denayer being named the PFA Scotland young player of the year.

The duo drew inevitable comparisons to the Johan Mjallby and Bobo Balde pairings of the Martin O'Neill era and the Marc Rieper-Alan Stubbs axis of Wim Jansen's 1998 title-winning side.

A 16-out-of-18 winning stretch from October to March was a good enough title charge and his emphasis on players' physique and robust style of play started to bear fruit as results followed.

A 2-1 win over nearest challengers Aberdeen at Pittodrie gave rise to the 'Ronny Roar' - the fist-pumping salute to the Celtic supporters that became de rigueur after every victory.

For two years it was a staple fixture as much as the huddle and a fitting encore for a man who was desperate to connect with the Celtic fans.

In that first season he also helped Celtic make it out of their Europa League group consisting of RB Salzburg, Dinamo Zagreb and Astra Giurgiu.

Deila's team were rather unfortunate to lose 4-3 to Inter Milan on aggregate in the last 16 of the Europa League courtesy of a Xherdan Shaqiri-inspired display at Parkhead in a 3-3 first-leg draw.

In the end-up, the title and League Cup were both won at a canter and it seemed a domestic treble awaited... or did it?

In the end it did not and Deila can lay claim to being the victim of a particularly bad officiating decision when Caley Thistle's Josh Meekings blatantly punched Leigh Griffiths' Scottish Cup semi-final shot off the line. It would have put Celtic 2-0 up, instead they went on to lose the match 3-2.

READ MORE: The secrets of Kieran Tierney's against-the-odds Celtic breakthrough by the men who witnessed it

It was the only real downer on the season after Champions League fell by the wayside. It was a mixed-bag of a transfer market but Celtic had to their credit recruited the likes of Craig Gordon and Denayer and supplemented them in the winter window with Stuart Armstrong and Gary Mackay-Steven. Just as notably, a clutch of fringe players were jettisoned too.

Deila also handed the keys to Paradise to a certain Kieran Tierney, who would net Celtic £25million further down the line. The Norwegian and John Collins deserve all the praise they can get for unearthing a true Celtic gem.

The second season turned out to be a nightmare. Despite retaining the title one wonders what might have happened had Griffiths not bagged 40 goals throughout the campaign. 

A second shock Champions League qualifying elimination - this time to Malmo - meant the Hoops dropped into the Europa League again.

Losing Van Dijk to Southampton coupled with Denayer's decision not to rejoin for a second loan spell left a gaping hole in the centre of defence while the Europa campaign itself ended with a bottom-of-the-table return in a group comprising Molde FK, Fenerbahce and Ajax.

The season arguably reached its nadir when a public spat was played out in front of the TV cameras between Kris Commons and the management team after the midfielder was substituted in a 3-1 defeat against Molde on Deila's return to his homeland.

In the domestic cups, Celtic succumbed 3-1 to Ross County in the semi-final of the League Cup at Hampden as they paid a heavy price for an early Efe Ambrose red card.

They were undone at the national stadium again - this time 5-4 on penalties - against Mark Warburton's Championship side Rangers in the Scottish Cup last four. 

That defeat, in essence, was the Deila era in microcosm as Celtic progressed to the latter stages but just simply failed to turn up and perform on the big occasions it mattered most.

The manager had taken the unusual step before the Scottish Cup loss to announce that he would be stepping down from managerial duties at the end of the 2015-16 season.

Deila, right, watches a young Kieran Tierney against Fenerbahce

By then, it was being reported that the squad contained several unhappy players. While recruitment was regarded to have been poor - Tyler Blackett, Scott Allan, Carlton Cole, Saidy Janko and Colin Kazim-Richards stick out - in reality the basis of the Invincible treble-winning side the next season was put in place with Dedryck Boyata, Ryan Christie, Jozo Simunovic, Erik Sviatchenko and Patrick Roberts all joining during Deila's last season.

Ironically, while it was the Norwegian more than any other boss in recent history who was charged with the task of winning the domestic treble for Celtic it was those who followed him who waltzed off with a succession of them.

Deila's detractors will state that he was tactically naive both at home but especially abroad. It could well be that, as an up-and-coming manager, he was simply promoted beyond his realm a bit too soon in his career to make a proper fist of a top job at a renowned European club.

The Norwegian won two Scottish Premiership titles and a League Cup with Celtic. He was also the first Hoops manager to get the club out of the Europa League group stages and into the knockout phase.

More than anything else, though, it was he who oversaw the development of players such as Tierney and Callum McGregor while helping fine-tune James Forrest and Leigh Griffiths.

These four - and arguably Tom Rogic - were all players whose contribution to the cause further down the line under other managers proved invaluable and immeasurable. He also helped turn Van Dijk into a powerhouse and ultimately one of the best defenders in world football.

The Hampden Scottish Cup semi-final defeat to Rangers which signalled his departure also ushered in the glorious Rodgers era. Every cloud and all that.

The Norwegian deserves to be remembered for more than just that painful defeat to Rangers and sparking the move for Rodgers, though.

Some eight years after his appointment he still strikes as a curious and enigmatic choice. It remains arguably the most interesting managerial experiment in the club's 134-year history.

Three trophies in two seasons, Europa League progress in one and several players put in place for an unprecedented period of dominance ensure history - and the Celtic fans - will likely always be kind to Deila. And they'll always have those Ronny Roars.

For those memories alone it is a case of 'tusen takk, Ronny', as they say in Norwegian. Or to put it more simply: a thousand thanks, Ronny.