They are known as Los Leones (The Lions) because their stadium was built near a church called San Mamés (Saint Mammes). Mammes was an early Christian thrown to the lions by the Romans. Mammes pacified the lions and was later made a saint.
The club is one of three founding members of the Primera División that have never been relegated from the top division since its inception in 1929, the others being Real Madrid and Barcelona. Athletic have won La Liga on eight occasions, fourth most in the history of the league. In the table of Copa del Rey titles, Athletic is second only to Barcelona, having won it 23 times. The club also has one of the most successful women’s teams in Spain, which has won five championships in the Primera División Femenina.
The club is known for its cantera policy of bringing young Basque players through the ranks, as well as recruiting players from other Basque clubs like Joseba Etxeberria and Javi Martínez. Athletic’s official policy is signing professional players native to or trained in football in the greater Basque Country, which includes Biscay, Gipuzkoa, Álava and Navarre (in Spain); and Labourd, Soule and Lower Navarre (in France). Since 1912, Athletic has played exclusively with players meeting its own criteria to be deemed as Basque, and has been one of the most successful teams in La Liga. This can be seen as a unique case in European football; it has gained Athletic both admirers and critics. The club has been praised for promoting home grown players and club loyalty. The Basque rule does not apply to coaching staff however, with several examples of non-Basque coaches both from Spain and abroad having coached the first team.
Athletic’s main rivals are Real Sociedad, against whom it contests the Basque derby, and Real Madrid, due to sporting and political rivalry. At various points in the club’s history, further Basque league derbies have been contested against Alavés, Eibar and Osasuna. Athletic is one of only four professional clubs in Spain (the others being Osasuna, Real Madrid and Barcelona) that is not a sports corporation; it is owned and operated by its club members. Source: Wikipedia