Cecebeck ("Beck" for short) was empowered after a weapon firing magical dust transported her to the Rock of Eternity. There she awoke Captain Marvel from a centuries-long sleep, and short afterward - after a further incident transported others there in the middle of a firefight - he imbued her with his powers for her own protection. Shortly afterward, she discovered her parents had been killed and the murderer, who had been given similar powers by the Three Faces of Evil, was attacking the Science Council who ruled her home planet of Binderaan. She eventually overcame him and trapped him in the Rock of Eternity, and Captain Marvel allowed her to keep the powers.
Some time later, when the 20th Century Captains Marvel had been injured in a car crash when Chain Lightning absorbed their magical lightning, their Uncle Dudley and Tawky Tawny, along with Ibis' wife Tana, attempted to use the mists of Time outside the Rock of Eternity to find a future Captain Marvel to help them. Tawky found Thunder, but she was knocked from his grasp by Black Adam, who went back with Tawky instead, much to his discomfort.
Falling randomly through time, she exited in the late 30th Century, at a weak point in the Rock of Eternity's history - when it was blown up by the Objective Order, a group attempting to destroy all magic. While she captured their leader, Doctor Savant, she was stranded in the 30th Century and joined the Legion until she could find a way to reconstruct the Rock and return to her home time.
Some time after, she and Sensor were attempting to recover Eternium when they were captured by Lord Pernisius, a landlord on Rimbor who, manipulated by Savant, was attempting to recover Eternium for himself to use as a personal power source, and exhausting the power of a large amount of Eternium in the process. Drugged, she mumbled "Captain Marvel" - and found herself back in her home time, in her foster parents' house in her Beck form. While glad to be home, she felt guilty over Sensor's plight, and wanted to be back home in both forms, and so returned to the 30th Century and her Thunder form.
Soon after, the Legion cornered Pernisius, and Thunder risked her life to let the Legion tap into the same batch of Eternium as him, and the Eternium-powered Live Wire and Spark used their now-magical lightning to depower Pernisus. The team then exhausted their Eternium powers pulling the rest of the Eternium to that spot - although it remained radioactive Eternium, rather than the Rock of Eternity.
After this, she commuted back and forth between the 30th and 90th Centuries until the Blight invasion. Traumatised, she resigned from the Legion and went home, though promising to return "some day".
Powers and abilities
Copies of Captain Marvel's powers, granted to her by Captain Marvel himself in the 90th Century: the Wisdom of Solomon, Strength of Hercules, Stamina of Atlas, Power of Zeus, Courage of Achilles and the Speed of Mercury (the last also allows her to fly). Exposure to Eternium (the shattered pieces of the Rock of Eternity), however, weakens her.
When she says "Captain Marvel", she returns to her powerless body. Since becoming trapped in the 30th Century in Marvel-form, returning to her powerless form also returns her to her home time and planet - although becoming Thunder once more returns her to the 30th Century.