A usurper is the person who does the taking — someone who has seized power, a throne, a position, or a title that they had no right to. It is a noun for a person, and it is always an accusation. You will find it thick on the ground in history writing and in stories: the king dies, his brother takes the crown before the young prince can, and for the rest of the book he is 'the usurper'.

The word is formal and rather old-fashioned in flavour, which is exactly why it feels at home in tales of kings and empires. Shakespeare's plays are full of usurpers. Fantasy novels and games borrowed it wholesale, so learners often first meet it there.

Though actually, the interesting part is that 'usurper' says more about who is speaking than about what happened. A man who takes the throne and rules for thirty years, wins wars, and is loved by the people is still 'the usurper' to the family he pushed aside — and simply 'the king' to everyone else. Once his grandson is on the throne, the history books quietly stop using the word. Nobody ever calls themselves a usurper.

Outside kings and thrones, the word is used more lightly in ordinary life, usually with a smile or a sharp edge: a new manager who takes a job everyone thought was yours, a younger singer who takes the older star's place at the top of the charts. Sports writers love it — the young champion is 'the usurper' of the old one's crown. There, the accusation is mostly play; nobody really thinks a rule was broken.