 Wang 's tale portrays Zhou as an aging itinerant <unk> with " a fame <unk> like thunder " throughout the underworld society of <unk> . He is made the sworn brother of the outlaw " <unk> <unk> " Lu Zhishen , a military officer @-@ turned @-@ fighting monk , who is , according to Hsia , first among the most popular protagonists of the Water Margin . He is also given the nickname " Iron Arm " ( <unk> ) , which carried over into the title of his fictional biography Iron Arm , Golden Sabre . While the tale fails to explain the reason for the moniker , it does mention Zhou 's ability to direct his <unk> to any part of his body to make it hard enough to <unk> the " Iron shirt " technique of another martial artist . Furthermore , Zhou shares the same nickname with Cai Fu , an executioner @-@ turned @-@ outlaw known for his ease in wielding a heavy sword . 
