Andrew Strauss resigned as England's Test captain and announced his retirement from professional cricket with immediate effect on Wednesday.
"After much thought over the last few weeks, I have decided to step down as England Test captain and announce my retirement from all forms of cricket," Strauss said in an England and Wales Cricket Board (ECB) statement issued ahead of a news conference at Lord's.
"It has clearly been a tough decision to make, but I believe that it is both in the best interests of the England cricket team and myself to step down at this stage," the 35-year-old, who played exactly 100 Tests, added.
"The driver to all this is I haven't batted well enough for a long time. I wasn't going to improve batting-wise, I've run my race," Strauss later told the news conference.
"It's one of these decisions when you know when your time is up."
"It is important for a captain to not be a passenger and that people are not speculationg whether you should be in the side."
Alastair Cook, already England's one-day captain and Strauss's opening partner in the five-day game, was announced as the new skipper of the Test team.
Strauss insisted his retirement had nothing to do with the ongoing England exile of star batsman Kevin Pietersen.
England dropped Pietersen, who hasn't played international cricket in any format since making 149 in the drawn second Test at Headingley, after he admitted sending "provocative" texts to South African players.
Some of these were alleged to have been critical of Strauss, who succeeded South Africa-born and raised Pietersen as England captain in 2009.
Strauss said he'd spoken to England coach Andy Flower about retiring "before the Kevin Pietersen situation reared its head".
His last Test was a 51-run defeat by South Africa at Lord's, his Middlesex home ground where he made his Test debut in 2004, earlier this month that saw England surrender their number one Test ranking to the Proteas.
Strauss scored 21 hundreds -- one shy of England's all-time record -- and led England to the top of the world Test rankings, a run that included home and away Ashes wins in 2009 and 2010/11.
Cook's first Test as captain will be the first of a four-match series in India in November.
The 27-year-old paid tribute to Strauss by saying: "Andrew's contribution to England cricket in recent years is evident to everyone who follows the sport but only those of us who have been lucky enough to share a dressing room with him are fully aware of his immense contribution to our success.
"He has been a fantastic captain, has led from the front for three-and-a-half years and is a true ambassador for the game.
"I know this can't have been an easy decision for him and everyone in the dressing room will be sad to see him go.
"I'm very excited by this new challenge, it is a huge honour to be appointed Test captain."
ECB chief executive David Collier said: "On behalf of the ECB and everyone involved in cricket I'd like to thank Andrew Strauss for his outstanding contribution to the game.
"Andrew's calmness and authority when dealing with some of the most difficult moments in our sport in recent times should be applauded and I have no doubt that his contribution as an ambassador for the game will be recognised by anyone who has had an opportunity to spend time with him."
Strauss has enjoyed modest returns with the bat in recent years and his 122 against the West Indies in May was his first Test century since November 2010.
He followed up with another century, at Trent Bridge, but averaged just 17.83 in six innings against the South Africans.
England's form in 2012 has been poor, with six defeats in 11 Tests culminating in a 2-0 series loss to South Africa, their first home reverse in four years.
Strauss was the third England skipper to be 'seen off' in as many tours of England by South Africa captain Graeme Smith after Nasser Hussain in 2003 and Michael Vaughan in 2008.
Andrew Strauss: Looking back
Strauss made his Test debut against New Zealand in 2004 at the Lord's cricket ground.
Strauss has played 100 Tests for England, out of which he captained the side in 50. He won 24 Tests as a captain.
Strauss led the English side to their No.1 Test ranking after winning back-to-back Ashes series. The loss against South Africa was his first ever series loss at home as a skipper.
He is the third English captain to step down after a series debacle against South Africa. Earlier Nasser Hussain (2003) and Michael Vaughan (2008) had resigned after suffering at the hands of Graeme Smith & Co.
Strauss hit 21 Test centuries and has 7037 runs under his belt at an average of 40.91.