When Per Mertesacker passed 30 years of age, his performances for Arsenal showed signs of being on the wane. He had never been famous for his pace, but his legs were showing signs of losing their power—as is usual for a man when he is in his thirties—during the 2014-15 season. He started to draw criticism after the Gunners went on a poor run of form following a 2-1 loss to Swansea, and became something of a scapegoat after he appeared to duck out of the way of Martin Škrtel’s goal-bound header in a 2-2 draw against Liverpool.

That moment at Anfield was probably the worst in Mertesacker’s time in North London. Before it the “BFG”, as he is affectionately known, had been largely popular at Arsenal but that alleged “duck” caused the tide to turn against him. Cries for a new centre-back became louder and louder, and throughout the season—even when the German’s performances started to improve—the opinion that he should leave the club became a more mainstream one.

In January 2015 Arsenal signed the Brazilian Gabriel Paulista who, despite not being able to speak English, performed well on every occasion he played for the first team last season. At the start of this season, Mertesacker was still preferred to partner Laurent Koscielny at centre-back. However, an injury to the German meant that the Brazilian got his chance to shine and he took it with some aplomb. It looked like the two-time FA Cup winner’s time as a guaranteed starter had come to an end.

After Gabriel’s red card at Stamford Bridge in September, things started to change back in Mertesacker’s favour. On his return to the starting XI he performed very well in a Capital One Cup game against Tottenham and in Arsenal’s 5-2 win at Leicester City. Koscielny’s minor injury in Arsenal’s Champions League defeat to Olympiacos meant that Mertesacker and Gabriel would play together for one game at home to Manchester United.

Since that famous 3-0 victory, the 31-year-old has regained his place as a starter; since that famous 3-0 victory, his performances have been far more reminiscent of the 2013-14 season where he was consistent, intelligent and a leader on the pitch.

Due to his lack of pace, Mertesacker has to have excellent positioning. In the last few months he has almost never been caught out of position, but unlike previous seasons there is a huge difference when he makes mistakes—he has a world class goalkeeper behind him. Should Arsenal’s defence be penetrated, Petr Čech is there to make the save which he does far more regularly than Wojciech Szczesny and David Ospina were ever able to. This insurance behind him has helped him relax and do his job of not allowing attackers through instead of worrying about catering for the man between the sticks.

Despite this, it is clear that Gabriel will be the regular partner of Koscielny soon enough. He is younger, quicker and hastily becoming a better all-round defender. In fact, he may already be superior. Yet Arsène Wenger starts his (on-field) captain ahead of his new starlet not just because of the latter’s struggle with the English language, but because the older thoroughbred is currently more reliable.

In individual games Gabriel has put in very strong performances; the kind of which Mertesacker is not entirely capable of producing any more. In these games he has not made any errors, which all of Arsenal’s centre-backs can do over 90 minutes, but crucially, he has been able to use his pace to take risks with positioning and make tackles which cancel out attacks earlier. This is what Koscielny is the master of, and if those two build up an understanding they can take it in turns to take these risks whilst covering each other should they make mistakes.

But football, and particularly looking at defenders, is not about individual games. One should wait after a long period of matches before passing a definitive judgement on one player. Gabriel can perform at a very high level when he is on form, but at the moment he is not able to perform at this level in every match. In fact, there have been a few matches this season where he has been quite poor—the 1-1 draw away to Norwich City springs to mind.

If you were to score Gabriel’s performances out of ten over a season, there would be plenty of “sevens”, a large number of “eights” and “nines”, but too many “sixes” and possibly even “fives” for a title-challenging team. Mertesacker, on the other hand, would not put in very many performances worthy of an “eight” or “nine”, but there would be so many “sevens” and so few weaker matches that his average score over the season would be very close to Gabriel’s.

But if Gabriel’s average score were to end up being higher, shouldn’t he be the first choice? On the contrary, Mertesacker would still be the preferred choice because if Koscielny’s partner can put in a “seven”, then Arsenal should be winning against almost any opposition. These consistent “sevens” would add up to more wins than the various “eights” and “sixes” of his team-mate.

And that is why Per Mertesacker has been an unsung hero this season. His consistency over the past few months has helped Arsenal string results together at an impressive rate. In Arsenal’s first choice starting XI the other ten have been and will continue to be more responsible for the team’s ascent to the top of the league, but without the consistency of the on-field skipper they may not have been able to pick up so many points.

At 31 years of age, he may not have long left at the top level of football, but this season could be one of the most important and successful of Mertesacker’s career. It could deliver the first league title of his career, as well as the first his team have won in over a decade, and though he is unlikely to set the world alight between now and the end of the season, he could still be the trusty servant in a team of royalty.