[2] He is nephew of Abel Caballero,[1] former minister of the Government of Spain and current mayor of Vigo, and member of the Spanish Socialist Workers' Party (PSOE).

[3] Following his obtention of a licentiate degree in Economic and Business Sciences from the University of Vigo, he earned a PhD in economics from the University of Vigo,[4] reading a dissertation titled Los fundamentos de la nueva economía institucional los determinantes institucionales de la política económica en España, supervised by José Carlos Arias Moreira.

Years later he would also obtain a PhD in political science from the University of A Coruña,[4] reading a dissertation titled Nuevo institucionalismo, gobernanza y economía política: El cambio institucional de la política española, supervised by Ramón Máiz [gl].

[5][4] He ran 9th in the Socialists' Party of Galicia (PSdG-PSOE) list vis-à-vis the 2003 Vigo municipal election.

[7] A renowned sanchista, Caballero won the PSG-PSOE vote to determine the Secretary-General of the organization in October 2017 running under a grassroots candidate profile.