The very next story in the comic is "Captain Marvel and the Amazing Case of the Code in Music!" This adventure introduces us to Mr. Banjo, a "master criminal, an ingenious plotter of crimes" who uses his banjo as a weapon of sabotage against the war efforts of the United States. Captain Marvel beats Banjo, thus defeating this malevolent maestro!
Both IBAC and Mr. Banjo made their first appearance in Captain Marvel Adventures #8 in different stories. They both appeared throughout Cap's golden-age comics and have even shown up in some present day ones as well!
*According to Mike's Amazing World of Comics