His keepers at the Oberhausen Sea Life Centre said his death was sad, but not unexpected, as octopuses usually only live a couple of years.
Manager Stefan Porwoll said: "His success made him almost a bigger story than the World Cup itself.
"We had all naturally grown very fond of him and he will be sorely missed."
"He was a great octopus, predicting such wonderful things. Will his last prediction come true? Yes it will! Bye bye Paul, the World Cup octopus."
Callum, 10, Falkirk, Scotland
"Paul, everyone that loved you will miss you. I will."
Natalie, 11, Leicester, England
"That is terrible news!"
Stephen, 11, Cumbria, England
"I was so devastated to hear about him dying, but I'm sure the legacy of Paul the octopus will live on."
Sannah, 11, Luton, England
"I liked Paul and saw him predicting the scores. I was shocked when I heard he was dead. I am very sad for him!"
Hwang-Jeong-Yeon, 11, Chukotka, Russia
"I'm really sad that Paul died, he must have been really fun."
Hayley, 11, Worcestershire, England
"Poor Paul, I'm so very sad."
Megan, 10, Queensland, Australia
"What a shame he died."
Jack, 10, London, England
"Well done Paul. Thank you for entertaining us. R.I.P."
Tom, 9, London, England
"It's really sad."
Nathan, 6, Tyne and Wear, England
"I loved that octopus! R.I.P. Paul!"
Cavan, 9, Swindon, England
"I can't believe he has died. He was a very famous and clever octopus."
Edward, 8, Yorkshire, England
"I loved Paul because he got it right every time. I love octopuses, they're so cute."
Eden, 8, Alicante, Spain
"He was a good octopus, I will miss him!"
Fatima, 15, Surrey, England
"R.I.P. Paul! You are an inspiration to all animals!"
Natalie, 10, Kent, England
"I will never forget you Paul."
Alice, 9, Surrey, England
"I found it odd that he knew who would win the matches. It's really strange how he was always right."
Helena, 11, Seine-et-Marne, France
"He was a very smart octopus, smarter than any other animal. Even though he predicted The Netherlands (where I was born) would lose, I still think he is incredibly smart. I hope his last prediction comes true. Goodbye Paul the octopus."
Sam, 11, Southampton, England
"I loved that octopus, it was so awesome. I can't believe it died!"
Jade, 10, Kuala Lumpur, Malaysia
"I like octopuses, especially him!"
Yin, 13, Cork, Ireland
"He was a true genius, the best octopus that ever lived."
Kiri, 10, Leicestershire, England
"I am sorry Paul died... how could this happen to this poor predicting creature? R.I.P. Paul. My thoughts are with you."
Theevan, 11, Hull, England
"R.I.P. Paul, maybe you'll meet my cat up there! Have a lovely afterlife!"
Daniel, 10, Scotland
"Sorry, I am going to miss you!"
Svenja, 9, Accra, Ghana
"R.I.P. Paul, you were a great inspiration to us and the star of the World Cup 2010."
Sami, 10, London, England
"He was the greatest!"
Hanad, 10, London, England
"Paul you were the best octopus I have ever seen. R.I.P. Paul, we all will miss you."
Zainab, 11, Birmingham, West Midlands
"Paul the octopus will rest in peace in heaven!"
Dinuka, 11, London, England
"I really liked Paul. May he join heaven. R.I.P."
Rachel, 13, London, England
"We all love you Paul, may you rest in peace and live a good life in heaven!"
Elivis, 12, London, England
"R.I.P. Paul we'll miss you. Good luck in heaven."
Benjamin, 10, London, England
"He's now a legend and will be remembered forever."
Eleanor, 12, Cambridge, England
"I thought Paul was amazing and didn't want him to go away, but at least he went peacefully."
Fahmida, 14, Manchester, England
"We will all miss him, but he will always stay with us even if we can't see him."
Lele, 11, West Yorkshire, England
"We will miss you very much Paul"
Brad, 11, Peterborough, England
"I loved him and thought he was smart."
Chloe, 11, Burnley, England
"This is terrible, I can't believe it happened. I hope he rests in peace.
Rebecca, 11, Stoke-on-Trent, England
"I thought he was an amazing octopus. But was it a coincidence that he picked the correct teams? Despite that I absolutely adore Paul and was sad to see him go."
Annie, 10, Wigan, England
"R.I.P. Paul, I will miss a lot. I never met you but I loved you!"
Sarah, 8, London, England
"Poor Paul! Still, at least he predicted the World Cup final correctly!"
Fiona, 12, Cambridge, England
Anhu, 8, Koli, Finland
"I'll miss him loads. I can't wait for his book to come out."
Isabel, 9, Hertfordshire, England
"Paul was a great predictor, but he's just an octopus - you'll get over it."
Sarah, 9, Cumbria, England
"I am really sad!!"
Megan, 10, Belfast, N. Ireland
"Paul you were my idol! I'll miss ya bud!!"
Alexandra, 11, Gwynedd, Wales
"Feeling very sad."
Anshu, 5, Berlin, Germany
"R.I.P. Paul. You were a true legend in Spain and the world. You will be truly missed."
Rebecca, 10, London, England
"R.I.P. We hope your prediction comes true that we will host the 2018 World Cup!"
James, 10, West Midlands, England
"R.I.P. Paul! You were a genius, we will miss you terribly."
Chloe, 12, Glasgow, Scotland
"Paul made us laugh and I think he was cool. R.I.P. Paul!"
Charlie, 9, Essex, England
"That's not fair! Oh, I feel so sorry for Paul!"
Kate, 10, Los Angeles, U.S.A.
"It's sad that he's died, but I think it was amazing how he could predict which teams would win in the World Cup!"
Bethany, 11, Lincolnshire, England
"Paul was great, he put life into watching football. We'll miss you terribly!"
Khadeejah, 13, London, England
"I loved Paul. May he rest in peace in octopus heaven!"
Emily, 12, Shropshire, England
"Poor Paul, he was very cool and smart. He was the best octopus ever. May he rest in peace."
Maria, 11, Londonderry, N. Ireland
"I am so sad he died. How did he know who was going to win?!!"
Katie, 13, Essex, England
"Rest in peace Paul, you were the best part of the World Cup. Paul should be the mascot for the next World Cup."
Ashley, 13, UK
"We will miss you lots Paul!"
Emma, 11, Co. Antrim, N. Ireland
"Bye Paul I will miss you! When I found out that he had died my mum and I were sad. He was so clever."
Ellie, 9, Northampton, England
"R.I.P. Paul the octopus."
Niamh, 10, Cumbria, England
"Noooooo, Paul was amazing! I'm really sad now."
Ellie, 11, Hampshire, England
"I will miss Paul R.I.P."
Munira, 11, London, England
"I think it's really sad that Paul passed away! R.I.P. Paul! I wonder who will predict the results for the next World Cup..?"
Pippa, 11, Norwich, England
"I am not very fond of octopuses, but Paul was a fantastic octopus."
Dorka, 10, London, England
"We shall miss you, you helped us to WIN!"
Lopo, 12, Barcelona, Spain
"Awwrrrr! Sad story, but Paul couldn't live forever could he?"
Amran, 11, England
"OHHHH!!!!! If Paul's dead, how will we know who'll win the 2014 World Cup in Brazil?! R.I.P. Paul."
Danny, 13, London, England
"I was SO upset about Paul dying. I'll definitely get the cuddly toys whey come out as well as watch the documentary and read the books!"
Daniel, 9, Norfolk, England
"Paul, you were a legend. Everyone will miss you. I even named my band Octopus Cool after him!! R.I.P."
Holly, 10, UK
"R.I.P Paul, you were really amazing. Thanks for predicting Spain would win! I'll miss you and I hope you are an inspiration to all the other octopuses out there!"
Carmen, 14, London, England
"I don't really watch the World Cup normally but this year I was fascinated by his psychic powers! R.I.P Paul!"
Eve, 12, Cheshire, England
"Rest In Peace!! We will never forget you, no Octopus will ever be like you."
Amy, 10, Bradford, England
"I'm really sad that he died but this is something that happens to everybody. I liked how he could predict the future."
Cliona, 10, Co. Sligo, Ireland
"Chantal he wasn't just any octopus, he was Paul the predicting octopus! I'm gonna miss him."
Michael, 12, Wales
"Paul is the greatest predictor of all time! I was very sad to find out what had happened. Paul shall always be remembered as the true predicting star of the World Cup."
Chris, 11, Scotland
"I am extremely upset to hear the news of his death. Hopefully he will be remembered for years, especially when the World Cup is on."
Jack, 11, Derbyshire, England
"I was crying when I heard this, it's so sad! I am sure everyone will miss him."
Alisha, 12, Stirling and Falkirk, Scotland
"Paul was very good at predicting the football World Cup. If only he was still alive he could maybe have predicted other things!"
Sophie, 12, Kent, England
"I loved him, he was right every time! But he didn't predict that one did he? (dying)."
Joe, 13, Cambridgeshire, England
"Paul the octopus was my hero! I watched every World Cup match he predicted. I will never forget him."
Kitty, 11, London, England
"Oh no what a shame! Well let's hope we all remember him as a great predicting octopus."
Scott, 10, Stirling and Falkirk, Scotland
"I really loved Paul the octopus. I cried a lot when I found out he had died and I don't even like football."
Rebecca, 10, Lancaster, England
"He's just an octopus just like any other ordinary octopus! What's the fuss about him being dead?"
Connor, 13, Essex, England
"Thanks for helping Spain win the World Cup! I supported them from the beginning and I was very happy when you said they would win."
Freya, 14, London, England
"He was amazing!"
Ellie, 10, Stockport, England
"It was sad news about this amazing octopus!"
Flora, 11, Cheltenham, England
"He will be missed by lots of people. He was one of the best animals ever!"
Beth-Rose, 11, Exeter, England
"Paul was one cool octopus. We will always remember him. R.I.P."
Elena, 12, Walloon Brabant, Belgium
"R.I.P. Paul! Me and all my family loved you, you were a very unusual creature. I will miss you!"
Neve, 9, Edinburgh, Scotland
"Who cares about a lucky octopus?"
Edward, 10, Yorkshire, England
"Aww...R.I.P. Paul! We will all remember you as the only animal ever to predict the World Cup correctly. We'll miss you."
Senichia, 12, London, England
"I think it is really dreadful that Paul the octopus has died. I was really looking forward to Paul predicting at the next World Cup."
Subhan, 10, London, England
"He was amazing!!! We loved you Paul! Bye amazing octopus!!!"
Anna, 9, UK
"I liked him because he said the right answers on the World Cup."
Luke, 9, Essex, England
"I thought the whole thing of him predicting the winner was a joke, but it is sad he's died. R.I.P. Paul."
Charlotte, 11, UK
"R.I.P. Paul my friend. I will miss you."
Patrick, 12, Glasgow, Scotland
"Why does anyone really care? He was just an octopus. At least the Sea Life staff will have had a tasty meal that night!!"
Tom, 12, Bristol, England
"It's just a silly octopus, what about all the thousands of animals killed in the oil spill in the Gulf of Mexico? Do they get their own comments page? People who say they are devastated about his death are silly - they never knew him!"
Lucienne, 12, Oxford, England
"Oh what a shame for Paul to die, I really liked him."
Faye, 8, London, England
"I can't believe he's gone. He was so cute and really smart knowing who would win the matches."
Leah, 11, Dublin, Ireland
"My mum was a huge Paul fan and is very sad."
Jack, 10, Hampshire, England
Amy, 14, Bournemouth, England
"We will miss him!"
Maqdus, 11, Luton, England
"R.I.P. Paul! You're an inspiration to other octopuses! We love you!"
Shona, 11, London, England
"It's sad that he's passed away. We won't forget him!"
Charlie, 9, Kent, England
"R.I.P. Paul. You will be missed"
David, 11, Peterborough, England
"I think Paul was a marvel of nature and it's sad to hear he has passed away."
Rebecca, 11, Buckinghamshire, England
"We will miss you loads, Paul!"
Megan, 10, Ireland
"That's really sad! He did a great job of predicting the scores! R.I.P. Paul the octopus."
Sofea, 11, Warwickshire, England
"R.I.P. Paul! You were the best octopus (no offence to others). We love you!"
Lily, 12, Swansea, Wales
"I believe that Paul was a fantastic octopus and I'm devastated to hear he's passed away. I hope people remember him forever."
Ayan, 13, London, England
"I feel sorry for Paul."
Saf, 10, London, England
"So sorry to hear the news."
Ashleigh, 11, Berkshire, England
"I feel really sorry for Paul. I found him extremely clever! How could such a terrible thing happen to poor old Paul?"
Simona, 9, London, England
"That's really sad! He did a great job of predicting the scores! R.I.P. Paul the Octopus."
Sofea, 11, Warwickshire, England
"It's just an octopus."
Chantal, 12, Essex, England
"So sad to see him go, I thought he was amazing and fabulous."