Wang 's tale portrays Zhou as an aging itinerant swordmaster with " a fame reverberating like thunder " throughout the underworld society of Jianghu . He is made the sworn brother of the outlaw " Flowery Monk " 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 " ( 铁臂膀 ) , which carried over into the title of his fictional biography Iron Arm , Golden Sabre . While the tale fail to explain the reason for the moniker , it do mention Zhou 's ability to direct his qi to any part of his body to make it hard enough to overpower the " Iron shirt " technique of another martial artist . Furthermore , Zhou share the same nickname with Cai Fu , an executioner @-@ turned @-@ outlaw known for his ease in wielding a heavy sword .