He serves as the inventor, fabricator and the mechanic of the TNT group. He moved to America and changed his last name from Grunt to Grunf to avoid detection, and is mentioned to also serve in Second World War. He is a former Luftstreitkräfte mechanic who fought in the First World War, and he defected from the German army after his mechanical incompetence caused the airplane of the Red Baron to crash. Otto Grunf is a naturalized German-born inventor. Despite this, he is one of the most trusted TNT agents. He is mostly at odds with Number One for abnormally poor salary and his tyrannical attitude, and he is usually attacked by Number One with his stick when Bob provokes him. Bob has a poetic side: he frequently tries to write books or poems that end up being rejected by even the worst publishers and/or ridiculed by other TNT members. He stopped berating them after they joined the TNT under The Great Caesar. Despite this, Bob refuses to follow the criminal career path and frequently berates his brothers for it, despite them being clearly more successful than Bob. He has three younger brothers, a set of triplets called Tim, Tom and Tumb, who are professional criminals and frequently try to use Bob as the scapegoat in their criminal schemes. He came from a family of criminals: his father died when he was a child, and his mother died after being riddled by machine gun fire during a botched robbery attempt in his teenage years.
