Former Essex team-mate Graham Napier...

Dai Salthaus: Alastair Cook in the 2010-11 Ashes in Australia was operating on a completely different level to anyone else in that series. Absolute masterclass. Would love to see him go out in style at The Oval. Cheers Chef!

Nick Compton
Middlesex and England batsman on BBC Radio 5 live

I presume it is something he has thought about for a while, and it will have been an incredibly difficult decision for him. It is a game he has given so much to.

I know how hard it is to bat at the top of the order. With his ability to stay fit and consistent, he has been a magnificent ambassador for the sport and the country will miss him terribly.

He has given everything to cricket and that takes its toll. Twelve years at the top of the sport is incredibly relentless and everyone has huge admiration for him and what he has done.

Lisa Sthalekar, former captain of the Australia women's team...

More from ECB chairman Colin Graves: "I would like to personally thank Alastair for everything he has given to the England team and also acknowledge the important supporting role his family has played in helping him make such a success of his career.

"He leaves the international arena with our warm best wishes and will, we trust, continue to grace our county game with Essex for many years to come."

Kenny: Favourite Cook memory? No contest - him answering his critics by laying waste to Australia in the 2010-11 Ashes. A mountain of runs!

Former England all-rounder Paul Collingwood writes on Instagram: "Alastair Cook retires from international cricket. He gave it everything and more.

"Huge respect for a guy that has achieved so much, it was a pleasure being out in the middle when you scored a lot of your hundreds for England! Thanks for fighting so hard.

"This pic was from his debut hundred in Nagpur when he flew in last minute to Marcus Trescothick. An incredible century that was to carry on for the next 160 test matches! #goat , external#cricket , external#england , external#proud , external#legend, external."

Jim in London: Cook is a legend of the game - imagine if he'd batted four! None of the others in that list of top 10 Test runs faced the brand new ball and fresh bowlers as regularly as Cook. I reckon that's worth a few extra runs over a career.

Cook hit 243 against West Indies at Edgbaston last summer but went through another lean spell before making an unbeaten 244 against Australia in the Boxing Day Test, his fifth double century.

More recently runs have sadly been more difficult to come by and he has passed 50 only once in 16 innings since then. This year he has been well below his prolific best, with 298 runs in nine matches at an average of 18.62, with a top score of 70.

Image source, AFP

Here's an assessment of Alastair from the moment he reached 10,000 runs, including interviews with Andrew Strauss, who says Cook will be "one of the greatest", Jimmy Anderson and Stuart Broad, who says "I am very proud to have played with him." Nice to be liked isn't it?

In 2016 he became the first Englishman to reach 10,000 Test runs (and here he is at Lord's presented with a handsome silver bat to commemorate the occasion), but England lost 4-0 in India that winter and Cook resigned as captain in February 2017.

Image source, Getty Images

Cook skippered England for many years of course, in a record 59 matches, winning two Ashes series and a total of 24 matches, a figure bettered only by Michael Vaughan's 26.

He first took the captaincy on the tour of Bangladesh, as Andrew Strauss took a rest, and registered scores of 173 and 109 not out.

When Strauss retired, Cook was handed the role on a permanent basis for the tour of India in November 2012 and scored three centuries as England gained their first series victory there for 27 years.

Image source, Getty Images

John: Cook's Test average is just that - very average. Look how he compares with those above him in the runs list.

Who agrees with John? An average of 44 over 160 Tests, not too shabby is it? #bbccricket or text 81111

He scored more than 1,000 Test runs in just nine innings between November 2010 and June 2011, helped by a double hundred, two other centuries and an average of 127 in the 2010-11 Ashes as England won the urn in Australia for the first time in 24 years.

Image source, Getty Images

Cook immediately demonstrated his suitability for the highest level when he flew to India at the last minute from an A tour in the West Indies to cover for Michael Vaughan and promptly scored 60 on his debut in Nagpur, followed by an unbeaten century in the second innings.

Image source, Getty Images

Adam in Suffolk: Alastair Cook is five days older than me. I was privileged to share a field with him once when I played against him during an U16s match. Since then he's been all over the world and scored 12,500 odd runs for England and I've managed 1,069 runs for the mighty Leavenheath CC! What a player, so much respect for the incredible career he's had.

Another big announcement today of course, although significantly less impactful on English cricket, with Chris Evans leaving his Radio 2 Breakfast programme. By coincidence, his first Radio 2 programme was announced the day after Alastair Cook's Test debut in March 2006.

Veteran South African Hashim Amla (pictured with Cook during the 2015-16 England tour to South Africa, which they won 2-1), will become the highest-placed batsman still playing. The 35-year-old is in 15th place on the all-time list with 9,022 runs from 119 matches.

England captain Joe Root is 63rd with 6,154 from 73 Tests and Indian counterpart Virat Kohli is two places lower on 6,098 in 70 matches.

Image source, Getty Images