What is the origin of the idiom "give the devil his due" and when to use it?

The idiom "give the devil his due" has its origins in the medieval legal system of England. During trials, the accused was often perceived as being in league with the devil. The phrase was used to mean that even the most despised or reviled individuals should be granted a fair trial and treated according to the established legal procedures. It emphasized the importance of upholding justice and ensuring that even the accused received their rightful legal rights and protections. It is used in various contexts or occasions where there is a need to acknowledge the positive attributes, accomplishments, or merits of someone who is generally disliked, controversial, or considered unfavorable.