nemesis
n. countablen. a person or thing that is a constant enemy or a very difficult problem to overcome. It often feels like they are specifically designed to defeat you.
n. a persistent rival or formidable opponent who is seemingly impossible to defeat. Often carries a connotation of inescapable retribution or poetic justice.
The local champion finally met his nemesis in the final match.
Public speaking had always been her professional nemesis, preventing her from seeking the promotions she deserved.
In classical literature, the protagonist's downfall is frequently orchestrated by a nemesis who embodies the very flaws the hero refused to acknowledge during their rise to power.
From Ancient Greek Νέμεσις (Némesis, “Nemesis, goddess of retribution”).
Often used with the possessive ('my nemesis', 'his nemesis') to indicate a personal and long-standing rivalry.