user: Q: De Villiers, 30, set the new landmark during an innings of 149 against the West Indies in Johannesburg.
He smashed eight fours and 10 sixes in beating the previous ODI record of 36 balls by New Zealand all-rounder Corey Anderson against West Indies last year.
"I was on 92 when I realised it was going to be close. I wasn't going to take singles in the nineties," he said.
"I got really fired up in the changing room and sort of played my knock before I even came out to bat.
"Aggression was the main thing for me today - I just wanted to go right from the start."
Chris Gayle's 100 from 30 balls in the Indian Premier League in April 2013 is the fastest century in cricket history.
South Africa scored 439-2 as they registered their highest ever ODI score, beating the 438-9 in a win against Australia in March 2006.
The total was just four short of the all-time ODI record score of 443-9 set by Sri Lanka against Netherlands in July 2006.
Openers Hashim Amla and Rilee Rossouw also both hit centuries but ODI captain De Villiers stole the show with his spectacular innings.
De Villiers raced to 50 off 16 deliveries to surpass Sanath Jayasuriya's 19-year record for the fastest ODI fifty.
He ended up with 149 off 44 balls, hitting nine fours and 16 sixes, the latter equalling the record for the most number of maximums in an ODI innings.
In the second of a five-match ODI series against Windies, De Villiers was eventually out when caught at deep extra cover with two balls left off the bowling of Andre Russell.
"He said he was going to have a look for one over," said Test captain Amla. "He is an amazing player."
Former England captain Michael Vaughan: "Have to say AB de Villiers is the definition of a cricketing genius. Absolutely incredible.
"When I watch him bat it reminds me that I really wasn't that good in comparison.
"And you still get some ex-players saying the game was better in the 1970s and 1980s."
Ex-England fast bowler Bob Willis: "AB de Villiers' record ODI hundred off 31 balls could make him the best batsman of all time.
"I've been saying for the last 30 years that Viv Richards has to be the best batsman of all time - even better than Sir Don Bradman in my book - but I'm going to have to reassess because this guy is something extraordinary."
Former South Africa batsman Herschelle Gibbs: "AB showing why he's simply the best."
Ex-India batsman Aakash Chopra: "I demand a DNA test of AB DeVilliers - this game is only for humans."

A: South Africa batsman AB de Villiers hit a century off 31 balls to record the fastest ever one-day international ton.


Q: Men are underdiagnosed and undertreated for anorexia and other eating disorders, despite making up about a quarter of cases, a UK study suggests.
Frontline health workers have a key role in identifying eating disorders in young men, they report in BMJ Open.
Men are under pressure to have the "ideal" body image, says a charity.
Researchers from the University of Oxford and University of Glasgow interviewed 39 young people aged 16 to 25, including 10 men, about their experiences of diagnosis, treatment and support for eating disorders.
They say young men with eating disorders were "underdiagnosed, undertreated and underresearched".
This is partly because the men themselves were unaware of the symptoms, despite purging, not eating for days or obsessive calorie counting, they said.
"Our findings suggest that men may experience particular problems in recognising that they may have an eating disorder as a result of the continuing cultural construction of eating disorders as uniquely or predominantly a female problem," said Dr Ulla Raisanen and Dr Kate Hunt.
One man said he thought eating disorders only affected "fragile teenage girls"; another said he thought eating disorders were "something girls got"; while one was told by his doctor to "man up".
Others said they often had to wait a long time for specialist referral and had sometimes been misdiagnosed.
GPs and other professionals such as teachers have a key role in improving the outlook for men with eating disorders by challenging misconceptions, the researchers said.
And men themselves needed the courage to "speak up to somebody and contact a health professional to tell them what is going on", Dr Raisanen added.
Eating disorders include anorexia nervosa, bulimia nervosa; and binge eating disorder.
One estimate puts the cost to the NHS of treating eating disorders at Â£70m.
Commenting on the research, Leanne Thorndyke, of the Beat eating disorders charity, said a wider section of society is coming under pressure over their body image.
"The pressures on body weight and body image are affecting a much wider range of people, which obviously includes men," she told BBC News.
Eating disorders are complex - with a wide range of different factors, including genetics and the environment affecting risk - as well as social and cultural pressures.
"There is more pressure on men from magazines with celebrities and male models to have the 'ideal' body image," she added.
"Boys and men tend to want to be bigger and more muscular and toned, which is a different ideal to women."
She said people are "bombarded by images every day from all angles, something that just wasn't there only a few years ago", which can "negatively impact some people".

A: Young men with an eating disorder are not getting the help and support they need because of a perceptions about a "women's illness", say researchers.


Q: The European Commission says clearing land in order to plant biofuel crops can often cancel out the environmental benefits of biofuel. In some cases forests are chopped down.
The EU is putting a cap of 5% on the food-based biofuel allowed in the renewable energy used in transport.
The EU's total renewable energy target for transport fuel is 10% by 2020.
The Commission will change the 2009 Renewable Energy Directive and the 1998 Fuel Quality Directive.
New biofuel installations will have to meet a minimum 60% threshold in terms of their efficiency in reducing greenhouse gas emissions.
BBC environment analyst Roger Harrabin says some environmentalists had supported the biofuel laws in the first instance, before the side-effects became understood.
The UN has appointed a special rapporteur on the right to food, Olivier De Schutter, who has sharply criticised the direct and indirect effects of biofuels on the poor.
Now the EU is trying to shift biofuel production from food crops to farm waste, algae and straw.
Clearing land to plant food for biofuel releases the greenhouse gas carbon dioxide (CO2) through ploughing and can involve deforestation, which reduces the "carbon sinks" - the trees that absorb CO2.
A spokeswoman for the poverty action group Oxfam, Tracy Carty, welcomed the EU's new 5% cap but said the proposal would not go far enough.
"The cap is higher than the current levels of biofuels use and will do nothing to reduce high food prices," she said.
"The British government must up the pressure on other European member states to scrap its current targets and end all support for biofuels. With close to 900 million people going hungry every day, we cannot continue diverting valuable food into fuel."
Earlier, the EU Commissioner for Climate Action, Connie Hedegaard, said: "We must invest in biofuels that achieve real emission cuts and do not compete with food.
"We are of course not closing down first generation biofuels, but we are sending a clear signal that future increases in biofuels must come from advanced biofuels."
The European Renewable Ethanol Association (ePURE) rejected the suggestion that biofuel crops were putting too much pressure on food production.
"Global grain use for biofuels is minuscule and nowhere near enough to inflate prices significantly. Singling out biofuels for blame for rising food prices is simply reckless and only serves to damage public confidence in good biofuels", said ePURE's Secretary General Rob Vierhout.
"Europe has enough grain to produce both its food and fuel needs," he added.

A:

assistant: The EU is changing its policy on biofuels to encourage energy production from waste rather than from food crops.