Graeme Swann one of England's greats - Michael Vaughan
England will find it very difficult to fill the void left by spinner Graeme Swann's retirement, says his former Test captain Michael Vaughan.
Swann, 34, announced his decision as England, who have already lost the Ashes, prepared for the fourth Test.
"Of the last 20 years, Swann is going to be one of the hardest to replace," said Vaughan.
The BBC Test Match Special pundit said Swann's "character, fun and energy" would be missed in the dressing room.
With 255 wickets at an average of 29.96, Swann retires as England's second most successful Test spinner.
Only Derek Underwood, with 297 scalps, claimed more Test wickets - and he did so in an international career lasting 86 matches over 16 years, compared with Swann's 60 in five.
Vaughan added that Swann would be "talked about in the same breath" as Jim Laker, the first bowler to take all 10 wickets in a Test innings, and Derek Underwood.
"England without Swann in the last five years, I just can't see how many series they would have won," added Vaughan.
Reaction to the timing of Swann's announcement has been mixed.
Former England seamer Angus Fraser told BBC Sport: "I am not sure what to make of Graeme's decision. You hear his statement, talking about the fact that physically he is struggling [and] he can't have the impact that he once had.
"But it just doesn't feel right to me to call it over in the middle of a series.
"He said he wanted to be part of an England team that won four Ashes series, so you make that commitment, and when it's over, you pull out."
But Fraser, who is now Middlesex's managing director of cricket, acknowledged Swann's overall contribution.
"He will be remembered, quite rightly, as an outstanding cricketer who has played a major role in England becoming a force in the international game.
"Everybody thought conventional off-spinners' days of effective bowling were over, but he has shown that a high-quality off-spinner can be a match-winner too."
Ex-England bowler Derek Pringle said he "should have seen the tour out as a senior player", but former captain Geoffrey Boycott described Swann's decision as "honest" and "brave".
In the first three Ashes Tests down under, Swann took only seven wickets at 80 runs apiece.
"He hasn't been right the whole series. He hasn't been the Graeme Swann we know," said TMS pundit and former England opener Boycott.
"I think it's very honest to say: 'Hey, I've shot it, that's it, I'm not going to be any good any more.' "It takes a brave man to do that."
Mick Newell, director of cricket at Nottinghamshire, said Swann's carefree demeanour belied a studious attitude to the game.
"He joined us with a reputation for not taking things seriously but I found him to be very thoughtful about his cricket and very committed to improving his game," said Newell.
"He knows how to perk up a dressing room and he was an outstanding character to have in a cricket team.
"Swanny has been a dominant performer in Test cricket for six years and it will leave a huge gap in the England team because there is no outstanding spinner quite ready to fill the place that he will leave."
Swann's opposite number in the Australia team, Nathan Lyon, paid tribute to his "unbelievable" fellow off-spinner.
"He's someone who I've looked up to a lot," Lyon said. "His career stats stand for themselves, he's been an unbelievable spinner and someone who I watched pretty closely in my time.
Australia pace bowler Ryan Harris said the announcement had taken him completely by surprise.
"I don't know what to say, I thought he'd bowled OK in the series, just without luck I guess," said Harris. "I feel we've played him very well, too.
"Something's obviously not quite right with him, or he's fulfilled whatever he wanted to do, but to me that's a huge shock."