England Test captain Andrew Strauss said his "race was run" as he announced his retirement from all professional cricket with immediate effect on Wednesday.
And he insisted his decision to quit had nothing to do with the fall-out from the ongoing England exile of star batsman Kevin Pietersen.
"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," Strauss later told the news conference. "I wasn't going to improve batting-wise, I've run my race.
"It's one of these decisions when you know when your time is up."
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.
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.
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.
But Strauss said he'd spoken to England coach Andy Flower about retiring "before the Kevin Pietersen situation reared its head".
Strauss's 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, who replaced Strauss as one-day captain after last year's World Cup, paid tribute by saying: "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."
Meanwhile England managing director Hugh Morris said he would meet with Pietersen and Flower in the coming weeks in a bid to discover the precise content of the text messages.
He was more forthcoming in praising Strauss who, after taking over as Test captain from Pietersen following his public rift with former coach Peter Moores in 2009, steered England through one of their most successful periods.
"He has been a great servant for Middlesex and England and an outstanding ambassador for the game, not just in England but across the world," Morris said.
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.
As a player, Strauss scored a century on Test debut, against New Zealand at Lord's in 2004 and in all scored 7,037 Test runs at an average of 40.91 and took an England outfield record 121 catches, mainly in the slips.
His 50 Tests as captain produced 24 wins, making him England's second most successful Test skipper behind Michael Vaughan.
"For me, personally lifting the (Ashes) urn in Australia was the highlight and it was always going to take a huge amount to beat that," said Strauss, who added he'd yet to decide on his future career.
"I go out with absolutely no regrets, I've had such an amazing career. I've achieved far more than I ever thought I was going to and that makes me feel very proud and very honoured to have represented England."
Asked how he'd liked to be remembered, Strauss, after saying he "hated" the question, replied: "That I played the game in the right way, adhered to my principles and if people remember me for that I'll be very happy."