What is the origin of the idiom "friend at court" and when to use it?

The term "friend at court" is thought to have originated in the Middle Ages, when people would often seek the help of powerful nobles or clergymen to get their way. This was especially true in the court of the king, where having a friend who could speak on your behalf could be the difference between success and failure. The phrase "friend at court" has been used in many different contexts over the years. It can be used to describe someone who has a connection to someone in power, or it can be used to describe someone who is able to use their influence to get what they want.