London - Alastair Cook has been so important to England that for several years one of the most pressing questions confronting the selectors has been finding a partner for their stalwart Test opener.
As England's all-time leading Test run-scorer prepares to retire from international cricket following this week's series finale against India, their task has been made a whole lot harder.
A total of 12 batsmen have tried, and largely failed, to fill the gap left by Andrew Strauss since Cook's fellow ex-England captain retired six years ago - a reminder of how tough it is to open at Test level.
Yet it is a challenge the 33-year-old left-hander, who grew up long before the Twenty20 revolution, has taken on ever since he scored a century on Test debut against India in Nagpur in 2006.
Cook is not an eye-catching batsman in the manner of England's David Gower or West Indies' Brian Lara.
But he has been a mightily effective one and a hugely reassuring figure to his teammates waiting to bat in the dressing room, having made more runs (12 254), hundreds (32) and appearances (160) than any other Englishman in Test history.
That Cook broke the record of Australia's Allan Border - himself a doughty left-handed batsman - for most consecutive Test appearances (153), a figure he has now extended to 158, is another tribute to his stamina.
And yet for much of his career, Cook, who came to prominence in 2005 when he scored a double hundred for Essex against Australia, has been fighting history as much as making it.
In an era of soaring Test batting averages, some observers say Cook's mark of 44.88 disqualifies him from the highest class, while others have noted that, unlike his mentor Graham Gooch, he did not score Test centuries against fast bowling of the calibre possessed by the West Indies' teams of the 1980s and 1990s.
But not being quite as good as Gooch is no disgrace, while it is hardly Cook's fault his international career coincided with a relative lack of great fast bowlers.
Another defence is that England play far more Test cricket than their major rivals.
In addition to the responsibility of opening the innings, the quietly-spoken Cook also shouldered the burden of being England captain - an honour he did not seek but diligently carried out.
He led England to home Ashes series wins in 2013 and 2015 despite the protracted saga of Kevin Pietersen's exile from Test cricket.
And it is hard to imagine England's 3-1 Ashes success in 2010-11 - their only series win in Australia in the past three decades - without Cook's mammoth tally of 766 Test runs.
Cook also led from the front in superb fashion when, as captain, he scored three hundreds to inspire England to a rare series win in India, in 2012.
But while he once saved himself from being dropped by England with a century against Pakistan at the Oval just prior to the 2010-11 Ashes, the south London ground is now set to witness the end of his England career, with Cook admitting Monday he had "nothing left in the tank".
This year has seen the Essex opener struggling for runs. He is averaging just 15.57 in the current series against India.
Cook was well aware of his own form as he reflected on a marathon 244 against Australia in Melbourne in December - his most recent Test hundred.
"To bat as badly as I did for pretty much two months and then for 10 hours bat as well as I've ever done is quite strange," said Cook just prior to England's post-Ashes series in New Zealand.
"There were moments when it was tough, you question yourself," he added. "'Am I still good enough to play at the real elite level?' Not that the hunger has run out but is it all worth it?"
Last weekend, even Gooch suggested his protege was "flatlining".
Yet the surprise is not that Cook's form dipped but that he has been able to perform at the top level for as long as he has done.
And for that, England have cause to be very thankful.