Lieutenant Bertie Seltzer is a teenage intern of the Soda Control Board under Mr. Fizz. In Operation: S.I.X., he was ordered by Fizz to prevent Numbuh 2, Numbuh 3 and Numbuh 6 from delivering a shipment of soda to the Yipper Playtime Pizza Palace. When the heroes successfully reach their destination, it is revealed, to the shock of everyone, that the shipment was actually the Delightful Children From Down The Lane's birthday cake, which Numbuh 2 was tricked into delivering to them.