Steve Costigan, like many of Howard's pulp characters, is an Irish-American from Galveston Texas. He became a sailor abord the merchant ship Sea Girl where he holds the rank of "able seaman".
He is an amateur boxer in the heavyweight class standing six feet tall and weighing 190 pounds. His brother "Iron" Mike Costigan is also a boxer who has actually had more success than Steve.
Steve also has a pet bulldog who he found as a stray in Dublin and he has named him Mike after his brother.