autoproclamarse

Used, often critically, for someone who declares themselves holder of a title or role without a formal process granting it — se autoproclamó presidente, campeón, líder. Extremely common in political journalism.

• Guaidó se autoproclamó presidente encargado de Venezuela en enero de 2019. — Guaidó declared himself interim president of Venezuela in January 2019.
• El equipo se autoproclamó campeón antes de que terminara el torneo. — The team declared itself champion before the tournament even ended.
• Varios líderes se autoproclaman representantes del pueblo sin haber sido elegidos. — Several leaders proclaim themselves representatives of the people without having been elected.

Always carries an implication that the title is self-given and not formally recognized — using it for someone legitimately elected or appointed is a factual misstatement, not just a style choice.

• politics Juan Guaidó se autoproclama presidente encargado de Venezuela — On January 23, 2019, opposition leader Juan Guaidó declared himself interim president of Venezuela, invoking articles 333 and 350 of the constitution — one of the most widely covered real-world uses of autoproclamarse in contemporary Spanish-language journalism.