Kroff was a Nazi agent who wore a rubber mask to disguise his face and whose headquarters was an abandoned brewery. His plan was to steal some government documents by arranging an attack by young Harry White on Walt Walters, father of the young heroes Yank & Doodle. The heroes captured Kroff and he was unmasked as the police chief. It also came to light that Kroff had tortured Harry to force him to do his bidding. Feeling compassion for the tortured youth, Walters arranged for the boy to be released into his custody and gave him a job as a messenger boy.