Sentence:  [A] onetime classmate in Kumamoto said, "I think Matsumoto is trying to create a closed society like the school for the blind he went to. He is trying to create a society separate from ordinary society in which he can become <WSD>king of the castle</WSD>." 
Meaning of the word marked with <WSD> tags:  An individual who assumes a position of greater importance, authority, or prominence than others.