When the Princess Diana was sent to Man's world to put an end to the mad schemes of the war-god Ares, the war-god's son Phobos decided to gain favor in his father's eyes by destroying the Amazon Princess. Phobos journeyed to the Cavern of the Gorgons, where he drove his smoldering hands straight into the mystical mater that was the Gorgon's heart. Using his breath to shape the molten material he'd extracted, much as the Princess Diana herself had been molded form humble clay, Phobos created a small statuette, the figure of a woman, which he then had delivered to the Boston home of Professor Julia Kapatelis who had become Diana's mentor in Man's World.
Late that night, as Julia sought to teach Diana the English language, the statuette came to life, assumed full human size, and set about to destroy Julia's home and the Amazon Princess.
The battle between the Princess Diana and the creature who now called herself Decay spread across the entire city of Boston, with Decay leasing a swath of ruin and destruction behind her as they fought. Diana herself almost perished at Decay's hand, until the Amazon finally entangled Decay in the strands of her golden lasso. Since Diana's lasso had been forged from the girdle of the goddess Gaea, she possessed the power of constant renewal. Thus, the golden strands continued to pout life into Decay, who was the embodiment of death, until that power consumed her. Screaming in frustrated rage, Decay quite literally exploded from the strain.
Decay was later cloned by Dr Julian Lazarus, and into this body the spirit of Decay entered it and lived again. Although this body was mortal and finite, the demoness looked for power sources that would extend her new existence within the cloned body. After locating one, she came up against Cassie Sandsmark, the newly appointed Wonder Girl. Decay's body was broken into fragments but not completely shattered. This act kept the demoness' spirit trapped within.