What is the meaning of More loyal than the king?

This sentence is used as an Idiomatic expression when you descirbe the integrity or honesty or law-abiding nature of a person. Such person exhibits exceptinal honesty in life and abide by the rules of land in letter and spirit.

The idiom means someone who unnecessarily behaves more concerned about matters that concern someone else and ought not to have been of such concern to him. Generally it is spoken about sycophants and cronies for their undue zeal and interest in matters owed directly to someone else.