During the Great Crisis, an inter-dimensional species called the Controllers created the Sun-Eater. The Sun-Eater would effectively bring an end to the Crisis. The core of the Sun-Eater is heavily shielded and is protected by a lethal gas cloud. As its namesake, the Sun-Eater seeks out suns and devours an entire star. As a result, the the planets that depend on the sun fall out of orbit and life perishes. The Sun-Eater was used twice and deemed the most devastating weapon and it was too dangerous to destroy or dismantle. Instead, it was deactivated and locked away in the Fenton Arms Depot on Cheyenne Delta. Its existence was classified.
In the 30th century, a renegade Controller reactivated the Sun-Eater. A Category 9 Containment Failure was broadcast and prompted an investigation by the Legion of Superheroes. Running on reserve power, the Sun-Eater was able elude the Legion and escaped the depot. It reached full power after absorbing Cheyenne Prime, a red dwarf star. The Legion opted to use Lightning Lad and Cosmic Boy to combine their powers and Ferro Lad would channel it into one blast to take out the core. Ferro Lad couldn't handle the power and missed the core. Meanwhile, the Sun-Eater charted a new course for Earth and the Sun.
Brainiac 5 concluded that the only thing that could destroy the core was a solar transducer. Its creation would require too much time. To expedite the effort, the Legion freed the Fatal Five from Takron-Galtos and recruited their help. Emerald Empress would open the Sun Eater's cloud, the Persuader would disable the core's force shield, and Brainiac 5 would launch the transducer. The primary conductor failed. Ferro Lad sacrificed his life to detonate the transducer and destroyed the Sun-Eater.