Twenty-three-year old Leonard Brown is unhappy being a paper pusher at the spy organization T.H.U.N.D.E.R. and is relieved when he is asked to become a field agent. The Inner Council asks him to wear the Thunder Belt, a girdle which will change his body's atomic structure and give him 100 times his normal strength. Anxious to serve his country, Brown agrees, although he can only use the belt for 30 minutes at a time. The Thunder Belt increases his body mass and strength, but causes an enormous energy drain. The belt has a built-in alarm that signals five minutes before the limit; at the half-hour mark it automatically shuts off.
After giving the belt five minutes to become attuned to his metabolism so that only he can use it, Brown punches down a brick wall and goes to work fighting international crime as Dynamo, one of the T.H.U.N.D.E.R. Agents.
Among his other powers are the ability to leap hundreds of feet into the air (coming down with the appropriate force) and survive a direct hit from bullets or any other projectiles save for armor-piercing shells.