An Earth girl adopted by the Eternals of Saturn's moon Titan after the rogue Eternal Thanos killed her parents, Heather was raised by Titan's Shao-Lom monks, whose tutelage awakened her latent psionic powers while helping her achieve physical and intellectual perfection. Unfortunately, she grew arrogant, a trait reflected by her adoption of the name Moondragon after she seemingly destroyed the cosmic demon Dragon of the Moon. The Dragon secretly survived inside her, bolstering and feeding upon the darker aspects of her personality.
Thanos's assaults on Titan drove Moondragon to Earth where she allied herself with various heroes and joined the Avengers. Her questionable ethics and massive ego gradually estranged her from most of her peers whom she sometimes mentally manipulated. This culminated in Moondragon telepathically forcing the Avengers to aid in her "benevolent" conquest of the war-torn planet Ba-Banis, but the Avengers ultimately subdued her and turned her over to the Asgardian Gods. They placed her in the custody of the Defenders, who helped her truly reform until the Dragon's growing influence turned her against them, resulting in the destruction of both Heather and the Dragon. Moondragon was resurrected by the Eternals and her cousin, Pam Douglas, who developed powers of her own and became Sundragon. Free of the Dragon's influence, Heather remains arrogant and self-righteous, but genuinely regrets her past misdeeds and wishes to be a force for good in the universe.
Moondragon has been a mentor to Hellcat, a benefactor to Jack of Hearts and a would-be lover of Quasar (who did not share her feelings), though her machinations have estranged all of them to some extent. For a time, Heather wielded the cosmic Mind Gem as a member of Adam Warlock's Infinity Watch whose members also included Drax, Heather's late father reborn in superhuman form; however, the Watch soon broke up, relinquishing their Infinity Gems.
A friend and admirer of the late Captain Marvel (Mar-Vell), Moondragon has acted as an ally and advisor to his son, Genis, the new Captain Marvel. This led to a brief romance with Marlo Chandler Jones, wife of Genis's partner, Rick Jones; but the Joneses soon reconciled, and Moondragon resumed her travels alongside new love interest Phyla, Genis's sister.