History of Athletic Bilbao
Meanwhile, sons of the Basque educated classes had made the opposite journey and went to Britain to complete their studies in civil engineering and commerce. While in the United Kingdom, these students developed an interest in football and on their return to Bilbao they began to arrange games with British workers. In 1898, students belonging to the Gymnasium Zamacois founded the "Athletic Club", using the English spelling. In 1901, a meeting was held in the Café García, which established more formal rules and regulations. In 1902, the two Bilbao clubs formed a combined team, known as "Bizcaya", in the first Copa del Rey. They returned with the trophy after defeating Barcelona in the final. This would lead to the eventual merger of the two clubs as "Athletic Club" in 1903. In the same year, Basque students also formed "Athletic Club Madrid"; this club later evolved into Atlético Madrid. The club's foundation date is a subject of debate among football historians. The club itself declares 1898, but others claim 1901 or 1903 as the true founding year.
Atlético Madrid
The club was founded on 26 April 1903 as "Athletic Club Sucursal de Madrid" by three Basque students living in Madrid. These founders saw the new club as a youth branch of their childhood team, Athletic Bilbao who they had just seen win the 1903 Copa del Rey Final  in the city. In 1904, they were joined by dissident members of Real Madrid. The side began playing in blue and white, the then colours of Athletic Bilbao, but by 1911, both the Bilbao and Madrid teams were playing in their current colours of red and white stripes. Some believe the change came about because red and white striped tops were the cheapest to make, as the same combination was used to make bed mattresses and the unused cloth was easily converted into football shirts. This contributed to the creation of the nickname, "Los Colchoneros".
However, another explanation is that both Athletic Bilbao and Athletic Madrid used to buy Blackburn Rovers' blue and white kits in England. In late 1909, Juanito Elorduy, a former player and member of the board of Athletic Madrid, went to England to buy kits for both teams but failed to find Blackburn kits to purchase; he instead bought the red and white shirts of Southampton (the club from the port city which was his embarkation point back to Spain). Athletic Madrid adopted the red and white shirt, leading to them being known as "Los Rojiblancos", but opted to keep their existing blue shorts whereas the Bilbao team switched to new black shorts. Athletic Bilbao won the 1911 Copa del Rey Final using several 'borrowed' players from Athletic Madrid, including who scored one of their goals.