Athletic Club Bilbao, commonly known as Athletic Bilbao or just Athletic, are historically Spain's third most successful team with eight championships.
Alongside Barca and Real Madrid they are one of three teams never to have been relegated from the top flight. That proud record has been in danger in recent years, partly because of the self-imposed rule which makes Athletic unique in world football - they only use Basque players.
Writing in the club's centenary book in 1998, Athletic president Jose Maria Arrate summed up the policy thus: "Athletic Bilbao is more than a football club, it is a feeling - and as such its ways of operating often escape rational analysis. We see ourselves as unique in world football and that defines our identity. We do not say that we are better or worse, merely different.
"We only wish for the sons of our soil to represent our club, and in so wishing we stand out as a sporting entity, not a business concept. We wish to mould our players into men, not just footballers, and each time that a player from the cantera (youth academy) makes his debut we feel we have realised an objective which is in harmony with the ideologies of our founders and forefathers."
The San Mames, Athletic's home is known as 'the cathedral'. The ever passionate Athletic fans fill it to the 40,000 capacity most weeks - though there are plans to move to a new 53,000-seater venue on the same site by 2015. They'll probably fill that too.
An eighth-place finish last season means Athletic have not been troubled by European football this term and they haven't played Champions League football since 1999, though there was a time when they were among the greats of Europe. In 1957, Manchester United flew to Bilbao in an old Dakota plane to play Athletic, then champions of Spain.
"The temperature on board was freezing," recalls United defender Bill Foulkes. "I had fallen asleep with my foot on the lever which controlled the heat. It was so cold that the chairman Harold Hardman had to be rushed to hospital in Spain suffering from hypothermia. He missed the game and the flight home because of me. The flight was bumpy and the cloud was so thick that the pilot couldn't find the runway. He asked us if we could see it.
"My impressions of Spain being sun and sand were based holiday posters at railway stations, so I was surprised that it was freezing with snow on the ground. It was our first season in Europe and we were unbeaten until Bilbao gave us a real going over in front of 60,000.
"The pitch wasn't good, it was covered in slush and mud and it got worse as the game continued. Bilbao had the best centre-half I'd ever seen, Jesus Garay. He was so good that he kept Tommy Taylor quiet for most of the game and I'd never seen anybody do that.
"The Basques were quicker and much fitter than us but whilst we lost 5-3, Matt Busby instilled in us a confidence that made us think we could still handle them back in Manchester. He was right, but first we had to get back.
"There had been a snowstorm and players had to brush the wings clean of snow so that we could take off. The flight home was awful and we had a terrifying landing when we refuelled at Jersey, which saw some of the lads turn green. I was not bothered one bit, I thought it was exciting and I still loved flying at that time."
The following season, the United plane crashed at Munich.
Athletic have won the league twice since being champions in '56, the Basques triumphing in 1983 and 1984. It's impossible to see them winning the league again, but their fans wouldn't have their Basque identity lost by restructuring. And they continue to develop young players through their famed cantera system at Lezama on the outskirts of Spain's sixth biggest city.
Iker Muniain, the 18-year-old winger has really developed since making his debut two year ago. Fernando Llorente is the best striker in Spain not playing in the Champions League while Javi Martinez is a Spain international central midfielder. Right-back Andoni Iraola has been watched by most of the big clubs of Europe.
With such quality, Athletic are fifth in the Primera Division, with a formidable home record and looking very comfortable for a Europa League spot. They'll have their work cut out trying to add points to their tally this weekend though - Joaquin Caparros's side travel to Barcelona on Sunday.