
Nemesis
Unbeatable Challenge
Use 'nemesis' for something or someone that always seems to defeat or outdo a person, often creating ongoing strife. 
Personal Opposition
'Nemesis' often signifies a particular person's long-standing rival, implying deep-seated competition. 
Pop Culture Reference
In stories, 'nemesis' is commonly used to describe the main antagonist or villain who opposes the hero. 