What term describes someone who is unable to be conquered or defeated?

The term that describes someone who is unable to be conquered or defeated is "invincible." This word conveys a sense of strength and resilience, indicating that no force or challenge can overcome the individual. In various contexts, such as sports, mythology, or literature, an invincible person embodies an unbeatable spirit, often inspiring others with their unyielding nature.

In contrast, the other terms used do not carry the same meaning. "Defeated" and "conquered" inherently suggest a loss or inability to maintain control over a situation, while "vulnerable" implies susceptibility to harm or defeat. This makes "invincible" the definitive choice for describing someone who cannot be overpowered or subdued.