Alastair Cook has resigned as England Test captain after a record 59 matches in charge.
The 32-year-old Essex batsman took the role in August 2012 and led his country to Ashes victories in 2013 and 2015.
However, during last year’s 4-0 Test series defeat in India he admitted to having “questions” over his role.
“Stepping down has been an incredibly hard decision but I know this is the correct decision for me and at the right time for the team,” said Cook.
“Playing for England really is a privilege and I hope to carry on as a Test player, making a full contribution and helping the next England captain and the team however I can.”
Cook is England’s highest run-scorer in Test cricket with 11,057, while his 140 Test appearances and 30 centuries are also England records.
England and Wales Cricket Board director of cricket Andrew Strauss, who Cook replaced as captain, said his successor was owed “a great debt of gratitude” by his country.
“He’s led the team with determination, conviction and a huge amount of pride over the last five years and his record stands for itself,” added Strauss.
“He deserves to be seen as one of our country’s great captains.”
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The ECB has started the process of selecting Cook’s successor, with his fellow batsman Joe Root regarded as the favourite.
Strauss said he hoped to make an appointment before England depart for a three-match one-day international series in the West Indies on 22 February, which will be led by limited-overs captain Eoin Morgan.
The team will only play limited-overs matches for the first half of 2017, with their next Test, against South Africa at Lord’s, starting on 6 July.
After the four-match South Africa series, England host the West Indies in three Tests in August and September before travelling to Australia for the Ashes in November.
Why has Cook stepped down?
According to Cook’s long-time mentor Graham Gooch, he was asked to make the decision now or wait until the end of this winter’s Ashes tour.
Speculation over Cook’s future first arose before the winter tour of India, when he said he was looking forward to a time when he was no longer captain.
Although England gained a creditable draw in the first Test, their performances deteriorated.
In the fourth Test they became only the third side to lose by an innings after making 400 or more batting first, a result that sealed a series defeat and after which Cook said he thought Root was “ready” to lead.
The fifth Test saw the tourists again beaten by an innings after hitting 477 batting first, this time with India piling on 759-7, their highest Test total and the largest made by any side against England.
In the aftermath, former England batsman Geoffrey Boycott called on Cook to step aside, while ex-captain Michael Vaughan said he expected the opener to stand down.
Cook always maintained his future would be decided in a regular post-series debrief with Strauss.
The former team-mates met to discuss the India tour in January, but Cook had already indicated he would like more time to consider his position, with Strauss keen to give his old opening partner ample opportunity to come to a decision.
However, despite being publicly backed to stay on by coach Trevor Bayliss and a number of players, the Essex batsman has opted to quit, informing ECB chairman Colin Graves of his decision on Sunday.
BBC cricket correspondent Jonathan Agnew
As England’s highest Test run-scorer, Cook has always been admired for his batting, but there have always been questions, particularly over his tactics.
He has been stubborn – an excellent quality for an opening batsman, not always ideal in a captain – and largely cautious.
The most difficult time was in 2014, which began with the Ashes whitewash down under, moved on to the Kevin Pietersen saga and was followed by a home series defeat by Sri Lanka.
Cook’s 2013 Ashes win as skipper is a highlight of his reign. So too, the triumph in South Africa in 2015-16 and the historic win in India in 2012.
Cook’s winning percentage of 40.67 is only the fourth best of the six captains to have led England in more than 40 Tests. It has been an up-and-down ride.
The extended period of time taken to mull over his future shows that Cook has made the right decision for him. He will be incredibly comfortable with what lies ahead. That is likely to be scoring many more runs for England.
Is Root a certainty?
Root, who was Cook’s vice-captain, made his England debut against India in 2012 and has won 53 caps.
The 26-year-old Yorkshireman is the overwhelming favourite to replace Cook, but England head coach Bayliss indicated last week that all options would be looked at.
Speaking to BBC Sport two weeks ago, Root said it was “hard to say” how he would deal with becoming England captain.
“I’ve got a lot of experience in Test cricket and it’s one of those things that you learn on the job,” he added.
Root said he would like Cook to remain in the Test team as “whether as captain or not he will be a massive leader within the dressing room”.
Former England off-spinner Graeme Swann has said he is “not convinced” appointing Root would be the right decision.
“Root is the outstanding candidate, but you wouldn’t want it to be a case of making your best player captain, only for it to backfire on you later,” said Swann.
“I want him to concentrate on being the best player we have ever had, rather than having his talent curbed by the pressures of captaincy.”
Ups and downs
Cook was always seen as the heir to former captain Strauss, who retired in 2012.
His first job was to manage the return of batsman Kevin Pietersen, who had been left out of the England side over allegations he had sent derogatory texts messages about Strauss to members of the South Africa team.
With Pietersen back, Cook’s first year in charge was a success, including a first Test series win in India for 27 years and the retaining of the Ashes on home soil.
However, England were whitewashed 5-0 in the return series in Australia in 2013-14, after which England decided to end Pietersen’s international career, a decision in which Cook played an influential role.
With Cook’s form on the wane – at one point the left-hander went almost two years without a Test century – and England struggling, he came under immense pressure in the summer of 2014.
After defeats by Sri Lanka at Headingley and India at Lord’s, the likes of Vaughan and Alec Stewart, another former England captain, called for Cook to resign.
Cook, who later admitted he came close to quitting, revived his tenure with 95 against India at Southampton, an innings that set England on the way to a 3-1 series win.
Although he was sacked as one-day captain in late 2014, he regained the Ashes in the summer of 2015 and led England to a 2-1 series victory in South Africa, the world’s number one team at the time.
In the summer of 2016, he became the first England batsman to reach 10,000 Test runs and spoke of his desire to lead on the Ashes tour of 2017-18.
However, he began speculation over his future with his comments before the India series.
The four defeats took him to 22 as captain, an England record, while eight Test losses in 2016 equals their worst calendar year.
What they said
Cook’s mentor Gooch, another former England captain, said he had told Cook to stay on.
“This type of sportsman only comes once in a generation, maybe less. He’s a great man and he’s still got great things to do for his country,” Gooch told BBC Radio 5 live.
Former England bowler Matthew Hoggard said Cook would be remembered “not only as a great leader but also as a genuinely nice bloke” and his captaincy had “evolved” over time.