BRENDAN RODGERS was in the final weeks of his reign as Liverpool manager. Goodwill was short in supply. It was teetering on toxic on the terraces as many felt he had overstayed his welcome.

The Reds travelled to Old Trafford for their fifth Premier League match of the season – a game that always means more than most. Victory there is special, three points to be savoured. And meek surrender is a serious black mark for any Liverpool manager.

It was four years ago this week – September 12, 2015, just 22 days before Rodgers was told his services were no longer required at Anfield.

The then manager set Liverpool up in an uninspiring 4-5-1 formation, with perhaps the most confusing of his decisions that day being the one to deploy Roberto Firmino in a wing-back role on the right flank.

The Brazilian, who had become Liverpool’s second most expensive player in history when he signed from Hoffenheim for £29million three months earlier, was withdrawn in the 65th minute, replaced by Jordon Ibe. 

Liverpool lost the game 3-1 and a spectacular strike from Christian Benteke was rendered meaningless.

“[Firmino] has yet to come anywhere near the pace of the Premier League,” a BBC report said that day. 

The Beeb scribe was not alone in his reservations about the big-money buy: “What does he do?”, had been a regular refrain from Reds in Firmino’s early appearances, with many fans worn from watching too many players that should never have pulled on the red shirt at close quarters. 

In Firmino’s previous game he had been substituted on the hour, having been a peripheral figure as Liverpool lost 3-0 at home to West Ham, the Hammers’ first league win at Anfield since 1963.

Meanwhile, the story went that the Brazilian was not strictly Rodgers’ man; that in fact the manager had to be talked into it, while his weapon of choice was Benteke. He only agreed to Firmino’s transfer when told he could also have the Belgian targetman, went the tale.

Four years on, with Jürgen Klopp now firmly embedded in Liverpool folklore, those early facts about Firmino seem barely believable given what we know now.

In an alternative reality there were mumblings about fees, questions about effort and worries about suitability. No more. Feelings for Firmino couldn’t be more different.

Now the Brazilian is much loved, from terrace to touchline, from players to pundit. From a spare part that seemingly had Rodgers scratching his head, Klopp now purrs about Firmino as “the engine” of the Liverpool team. 

Every week someone somewhere describes him as “underrated”. In all honesty, who doesn’t rate him?

Early into the job at Anfield, Klopp revealed how pleasantly surprised he was that Liverpool had Firmino on board.

"Nobody [at Liverpool] asked me about him but he was a player I thought was one of the best in the Bundesliga so, when I saw that Liverpool had signed him, I thought: 'How could Liverpool do this?'

"They were not in their 100 per cent best moment and other clubs would have spent more on him so I thought immediately: 'What a good transfer for them.' I thought they had made a good signing because I felt pretty sure clubs would have paid a lot more for him.”

Klopp had witnessed Firmino’s work first-hand, with the forward, now 27, spending four-and-a-half years in the Bundesliga before he was transferred to Liverpool. Behind the scenes at Melwood, they perhaps knew even more, having scouted Firmino since his teenage years, according to Melissa Reddy, writing for Joe. 

Five Premier League games into Klopp’s tenure, those that hadn’t done their research or watched him play in Germany suddenly saw for themselves what all the fuss was about.

Firmino not only scored his first goal for Liverpool, he forced an own goal, he set up another, he dovetailed perfectly with Philippe Coutinho. He could have scored a hat-trick and he worked harder than anyone on the pitch.

Liverpool had won 4-1 away at Manchester City, a first league win there in seven years at the time. It could and should have been more convincing. It was only 70 days after Firmino’s bizarre wing-back appearance at Old Trafford.

That game came at the end of November, yet Firmino finished the season in double figures, scoring 11 in his debut season. In the three seasons that have followed, he has notched 12, 27 and 16 goals.

His overall statistics for The Reds read 198 appearances, 68 goals and 50 assists. But that doesn’t tell the whole story fof what Firmino has become for this Liverpool side. The question has now shifted from “what does he do?” to “what is he?”. He might wear a number nine on his back and he is no slouch at finding at the net, but he is no-one’s definition of the archetypal centre forward. Is he a 10 then, a false nine? Why do we see him almost in an eight position at times?

The truth is he’s a combination of everything – a mix that contributed to Daniel Sturridge kicking his heels and Philippe Coutinho heading for pastures new. 

He’s the hard-running forward who will chase and harry the defender looking for time to kick off a move. He will track, tackle, fight for the ball in the air and get his hands dirty in midfield. But he’s also the creator and a finisher. He almost managed both in his recent man-of-the-match performance against Burnley; feeding Mo Salah, watching his team-mate mis-control and then, having followed his own pass in, latching on to the lapse to put it in the back of the net.

And he’s relentless at the lot of it – always on the move, always fighting fire, and always quick to spot an opportunity to transform defence into attack. When Gini Wijnaldum tried to replicate his job for one day only, he didn’t fancy the position on a permanent basis. Few would. Because few are capable of it.

Liverpool have won without Firmino, famously so against Barcelona at Anfield, but no one who watches the side regularly would claim The Reds are a better side without him. There isn't a player approaching like for like in Klopp’s squad and that may go some way to explaining the heaps of praise manager and team-mates regularly throw in his direction.

Klopp summed it up, saying: “He is a very important player, a connecting player, a finisher, a fighter, a defender, the first defender – that is important. A lot of things he is good at are very important for us.”

It’s a long way from the boy lost on the flank in Manchester. And it appears Firmino and manager haven’t finished just yet as ambition abounds.

Tied down on a long deal, seemingly happy and relaxed and playing fantastic football, the ever-ready Firmino now looks like he is set on scoring more goals this season. Already he has attempted 17 shots at goal – more than any other player in the Premier League.

Goals will likely follow, as will assists, recoveries, tackles, showboating and the rest. 

Once a wing back, now a flying forward, Firmino’s arguably the most relentless number nine in Liverpool since The Beatles said it on a loop on The White Album.

The Kop will keep on bouncing to Bobby’s beat, and the team will too.