What a boss says is absolute.
That politician is the leader of the party.
These days, the word "leader" tends to be used in the political sense.
Someone who has territory under their sleeve is the leader. They're the boss of all this territory because they say so, and because they shoved it all into their big sleeves.
This is a jukugo word that uses the on'yomi readings of the kanji. You've learned them already, so you should be able to read this on your own!