Sentence:  They were disturbed by his idiotic bravado - as , when his bodyguard , Yankee Schwartz , complained that he had been snubbed by Dave Miller , a prize-fight referee , <WSD>chieftain</WSD> of a Jewish gang and one of four brothers of tough reputation , who were Hirschey , a gambler politician in loose beer running league with Torrio and O ' Banion , Frank , a policeman , and Max , the youngest . 
Meaning of the word marked with <WSD> tags:  the leader of a group of people