What is the origin of the idiom "a law unto oneself" and when to use it?

The origin of the idiom "a law unto oneself" can be traced back to the concept of self-governance and personal autonomy. While it is difficult to pinpoint a specific origin, the phrase embodies a philosophical idea that individuals have the ability to establish their own rules and principles, separate from external laws or societal norms. This phrase is used when someone consistently does things their own way, based on what they think is right, without caring about what others say or any rules from outside.