IN OCTOBER 1996, when Arsenal football club’s latest manager began his tenure, fans of “The Gunners” could be forgiven for grumbling. Apart from his name, there was little about Arsène Wenger to suggest that he would be a good fit. Only three foreigners had ever managed in the Premier League. Mr Wenger, a cerebral Frenchman with a degree in economics and a modest playing background, had almost nothing in common with his grizzled British peers. He had guided Monaco to a French league title in 1988, but had spent the previous two years in the footballing wilderness of Japan. The Arsenal squad that he inherited were a notorious bunch of alcoholics and drug addicts. The British press scorned his appointment.

Nobody could have expected “Le Professeur” to survive for 20 years. In that time, Mr Wenger has become Arsenal's most successful manager, the third-longest serving coach in English footballing history, and arguably the Premier League's most important innovator. His reforms at Arsenal were immediate. He turned a diet of pills and booze into one of protein and broccoli. He transformed a side known for turgid defence into one feared for its swashbuckling attack, by supplementing an experienced British core with flamboyant European youngsters. (Your correspondent, a lifelong Arsenal fan, was lucky enough to see young Frenchman and future star Thierry Henry score his first goal for the club in 1999.)

Success came quickly. Arsenal interrupted Manchester United’s monopoly of English football and completed a rare domestic “double” in 1998, winning both the league and the FA Cup, England’s main knockout competition. They repeated that feat in 2002 and collected the FA Cup in 2003 and 2005. The pinnacle of Mr Wenger’s achievements came in 2004, when Arsenal’s “Invincibles” won the league title without losing a single game—a feat only equalled in English history by Preston North End in 1889.

But though the first half of Mr Wenger's tenure was remarkable for his accumulation of silverware, the second half has been notable for a lack of it. Between 2005 and 2014 Arsenal did not win a single major trophy, the club's worst drought since the 1960s. The chief cause was economic. In 2001 the club announced its intention to leave its Highbury home (capacity: 38,400) and build a modern stadium with 60,000 seats, costing £400m ($500m). A group of banks purchased bonds worth £260m from the Gunners—on the condition that Mr Wenger would stay for five more years.

The new ground opened in 2006, by which point English football had changed forever. Roman Abramovich, a Russian oligarch, purchased Chelsea in 2003. He splashed out more than £400m on the players who won consecutive league titles in 2005 and 2006. The era of extravagant tycoon ownership had begun. By 2008, Liverpool and both Manchester clubs had also been purchased by foreign magnates.

Arsenal were wary of relying on unsustainable injections of cash and rebuffed similar approaches. In 2009 UEFA, which governs football in Europe, announced that teams would be punished for spending more than they earned. With no handouts from the boardroom, Mr Wenger had to finance the stadium by auctioning his Invincibles and sold four consecutive club captains. Between 2007 and 2013 he earned £253m (in 2016 prices) from transfers and spent just £207m, creating a surplus of £46m (see chart). In the same period Liverpool, Chelsea and the two Manchester sides ran a combined transfer deficit of £1 billion. The Frenchman fought for scraps on the second-hand market and relied heavily on young players poached from other teams. These makeshift squads rarely challenged for titles and struggled to cope with the new defensive rigour imported by Chelsea manager José Mourinho. They clung onto a top-four position each season, which secured them a place in the Champions League (Europe’s major knockout tournament) and much-needed television revenue.

It was only in 2013, two years after American sports tycoon Stan Kroenke had purchased a controlling share of the club, that the lean spell ended. The Gunners paid £40m for Real Madrid’s playmaker Mesut Özil and £36m for Barcelona attacker Alexis Sánchez the year after; they won consecutive FA Cups in 2014 and 2015. This summer Mr Wenger has spent a further £96m on players, and has assembled his strongest squad in a decade. His current contract runs out at the end of the season, however, and betting markets give him just a 10% chance of winning the league this time around. Despite turning down numerous offers to manage Europe’s biggest clubs in the past, it is possible that Le Professeur will be imparting his wisdom elsewhere next year. How then would his reign at Arsenal be remembered?

Mr Wenger’s first decade will be known for footballing triumph: he failed only in his quest for the Champions League, which he came within 15 minutes of winning in 2006. By 1999, this newspaper was already analysing “the nature of his success”. His second decade will be recalled for financial reasons. Granted, he kept the Gunners at the right end of the league table—and above local rivals Tottenham Hotspur—each season while selling off his best players: between 2000 and 2013 his net transfer spend was just £1m. But he also had the benefit of a substantial wage bill, which correlates very closely to on-field success. Given that his squad has typically been paid 60% more than Tottenham’s, and now earns as much as the players at the two Manchester clubs, Arsenal ought to have competed at the very highest level. As the Swiss Rambler, a footballing finances blogger, has shown, they now have the seventh-biggest revenue of any club and a cash reserve greater than that of Real Madrid’s, Barcelona’s and Bayern Munich’s combined. They have come within ten points of the league title just twice since their unbeaten season, and have failed to reach the quarter-finals of the Champions League six years running.

In 1999, we wrote that the Gunners’ love of their manager “would fizzle if the team flagged”. In the last three years, some fans have turned up to games with signs pleading “WENGER OUT”, citing his stubbornness in the transfer market and on the tactics board: the deft pass-and-move style that allowed Arsenal to dominate 15 years ago occasionally leaves them vulnerable against burly opponents. It would be a shame for a devoted servant to depart in such an abject manner. Aside from his achievements (or lack of them), Mr Wenger is known for his thoughtfulness, loyalty and generosity. These are rare qualities in the cut-throat world of modern football, in which the median tenure of current managers is less than one year. He might yet stay a couple more. But if he does leave this season, few would begrudge him a final, improbable success.