"My liege" is an archaic expression often found in Shakespeare plays. It's basically equivalent to "My lord" . It was said to the king or a nobleman whose orders you had to follow.

Yes, it refers to both. Here's the explanation: http://www.thefreedictionary.com/liege

"My liege" is a way to address royalty though it was usually used by the court and serfs mostly. A legion serves people.