[3] Under his presidency, the club officially absorbed their city rivals, Bilbao FC, and won its first two Copa del Reys titles.
[4][5] Being the son of a well-off family in Bilbao, Careaga was sent to Britain to complete his studies, where he developed a deep interest in football.
[6][7] Although it was formed in 1896, it was not until 30 November 1900 that the Bilbao Football Club was officially established in a meeting held in the house of industrialist José Luis de Villabaso (1852–1917) in the Biscayan neighborhood of Algorta.
[11] He only played in the final on 15 May, forming a defensive partnership with Athletic's Perico Larrañaga to help his side to a 2–1 victory over Joan Gamper's FC Barcelona.
[3] In the following month, on 8 April 1903, Athletic won its first-ever Copa del Rey title after beating Madrid FC in the final with a 3–2 comeback victory.
[14] Despite winning their first title at the national level, the recent merger with the whites of Bilbao FC, and the promise of forming a thriving society, at the end of the year the club faced a sporting crisis as they found themselves without significant rivals in its territory.