Athletic Club, founded in 1898 in Bilbao, is one of the most singular institutions in world football. The club's defining feature is the "cantera" (homegrown) policy: Athletic field only players who are Basque by birth, raised in the Basque region, or who came through Basque football clubs' youth systems. This rule has been adapted but never abandoned — it covers seven Basque-province academies including those of Real Sociedad, Osasuna and Eibar. Athletic remains one of only three clubs (with Real Madrid and Barcelona) never to have been relegated from La Liga since the league's 1929 founding.
The club's domestic golden era spanned the 1930s, with four consecutive Copa del Rey triumphs (1930-33) and three La Liga titles (1929-30, 1930-31, 1933-34). The post-war years saw a similarly strong run with three more league titles (1935-36, 1942-43, 1955-56). Athletic's modern flagship achievement is the 1983-84 Spanish double — La Liga and Copa del Rey — under Javier Clemente, with iconic players like goalkeeper José Ángel Iribar, controversial defender Andoni Goikoetxea (nicknamed "the Butcher of Bilbao"), and striker Manu Sarabia. Ernesto Valverde later defined the club's modern identity through multiple stints.
Athletic's 24 Copa del Rey titles place them second only to Barcelona in Spanish cup history. The club moved from the historic San Mamés (1913) to the new San Mamés (2013) in the same location, with capacity 53,289. The 2024 Supercopa de España title — the first major silverware in 40 years — marked a new chapter under Ernesto Valverde, supported by Iñaki and Nico Williams (the Williams brothers), Oihan Sancet and Unai Simón. The Basque Derby (Euskal Derbia) against Real Sociedad is one of football's most cordial fierce rivalries, with shared cultural identity tempering the on-field intensity.