What has been happening in North Korea recently is straight out of the "Hereditary Dictatorship for Dummies" handbook. Kim Jong Un, the pudgy young heir to the leadership of one of the world's last communist states, is removing powerful people who were loyal to his father and replacing them with men (it's always men) who owe their advancement only to him.
Vice Marshal Ri Yong Ho, the chief of the North Korean Army until late last week, was not disloyal to the new boss. On the contrary, Ri's support was vital in ensuring a smooth transition after the death of Kim Jong Il, the old boss, and he gave it unstintingly. But in the end the vice marshal didn't owe everything to Kim Jong Un, so he had to go.
In his place, Kim has promoted a man nobody had ever heard of before. His name is Hyon Yong Chol, but you don't have to remember it unless you really want to. The point is that Hyon will have annoyed a lot of other generals in the army because he has been promoted over their heads, and so he is absolutely dependent on the good will of the young master.