Since his first appearance, Galactus has been a persistent and looming threat to the denizens of the Marvel Universe. Cursed with an unquenchable hunger, the arrival of the world eater is generally considered a planetary death sentence, most often identified by the appearance of his heralds: cosmically imbued servants who seek out plentiful planets for the ancient being to devour.
While the most famous of these heralds is undoubtedly the tragic hero the Silver Surfer, others have filled this role throughout subsequent years, some more successful than others. While these heralds differ in physical appearance and personality, they all share a common trait of being some of the most powerful characters in the Marvel Universe.
The Destroyer
As one of Thor's coolest comic book villains ever, the Destroyer was traded to Galactus by the God of Thunder in exchange for the freedom of his then-current herald, in whom Thor had identified an inherent heroism. In contrast to most heralds of Galactus, the Destroyer had no prior personal identity and operated specifically to the whims of its wielder, which theoretically should have been a perfect fit for uncompromising cosmic devourer. Instead, Galactus was unimpressed by the Destroyer's methodical approach and didn't hesitate when Loki offered to take the ancient armor off his hands.
Red Shift
Not much is known about Red Shift before becoming a herald of Galactus, but he showed an unwavering loyalty towards the planet-eater during his limited tenure. Channeling his power cosmic through his swords, Red Shift was a formidable threat in combat, but his chosen weapons also sealed his own fate. During a battle with the Silver Surfer, Red Shift was forced through a dimensional wormhole and disarmed. Separated from his cosmically empowered swords, he was unable to follow when the Surfer abandoned him in this adjacent universe.
Air-Walker
A decorated Xandarian soldier and member of the Nova Corps, Gabriel Lan dedicated his life to the pursuit of adventure. When approached, he eagerly accepted Galactus' offer of cosmic power and the opportunity to explore the universe and was transformed into the Air-Walker. While journeying with Galactus, Air-Walker befriended the devourer and served him faithfully. He eventually sacrificed his life in service of his master when Galactus was attacked while weak and unable to defend himself.
Lamenting the loss of his trusted companion, Galactus attempted to transfer the Air-Walker's consciousness into a robotic replica, but the replacement lacked the original's personality and passion for exploration. Distraught, Galactus abandoned the Air-Walker automaton on Earth, where it eventually fell into the hands of the enemies of the Fantastic Four.
Firelord
Another Xandarian of the Nova Corps and friend to Gabriel Lan, Pyreus Kril spent years tracking Galactus' ship across the universe, determined to rescue his ally. Upon encountering him, Galactus was impressed by Kril's persistence and bravery. After offering to reveal Lan's fate in exchange for Kril becoming his new herald, Galactus granted Pyreus the power cosmic, and he became Firelord.
As Firelord, Kril primarily manifested his power cosmic as a "stellar flame," effectively operating as a living sun. He could project and manipulate heat, light, and gravity, sufficient to burn through most earthly matter. Firelord's tenure as a herald of Galactus was brief, however, and he was liberated when the Asgardian Thor, recognizing Kril's inherent nobility, traded the Destroyer armor for his freedom.
Invisible Boy
Most fans are aware that Susan Richards, the Invisible Woman, is the most powerful member of the Fantastic Four. When Galactus came to Earth intent upon transforming her into his newest herald, he instead discovered that she and her brother, the Human Torch, had recently swapped powers. Undeterred, Galactus instead selected Johnny, who at this point had begun calling himself the Invisible Boy.
Initially overwhelmed by his new cosmic abilities, Johnny quickly adapted and began seeking out uninhabited planets for Galactus to consume. His seeming loyalty to the world-eater was eventually revealed to be a distractionary tactic, however, allowing his teammates time to devise a means of removing both Galactus and Johnny's cosmic energies, reverting both to their original forms and temporarily neutralizing the ancient threat.
Frankie Raye
With powers almost identical to the Human Torch, Frankie Raye was an ally to the Fantastic Four, eventually joining their ranks as the team briefly considered changing their name to the "Fantastic Five." When Galactus once again arrived on Earth, Raye's tenure with the FF was cut short as she volunteered to become his newest herald. Like the Air-Walker before her, Raye, now dubbed "Nova," befriended the cosmic devourer, loyally serving him while gradually losing touch with her humanity.
Despite volunteering to serve Galactus to save the Earth, Raye's tenure as a herald led her to become apathetic towards the destruction he caused. While her initial goal was to only seek uninhabited worlds, she nonetheless eventually began leading her master to populated planets, including the homeworld of the alien Skrulls. After serving as a herald for years, Raye was finally reminded of her past morality by the Silver Surfer, who saw in her a kindred spirit. Galactus, displaying his own rare mortal emotions, became jealous of Raye's relationship with the Surfer and dismissed her from service, citing her ineffectiveness as a herald after she once again began refusing to lead him to inhabited worlds.
Stardust
The most fanatical of Galactus' heralds, Stardust worshipped the eater of worlds like a god. To this end, she not only sought new planets for him to consume but also attempted to hunt down and eliminate the survivors of worlds already devastated by her master.
A member of a race of beings composed of pure energy, Stardust's cosmic empowerment by Galactus effectively made her immortal, as she gained the ability to manipulate the very energies from which she was comprised. She was able to reconstitute herself from any injury, as well as alter her form at a molecular level for a variety of effects. Though she likely would have willingly served Galactus for an eternity, Stardust was separated from her master following a battle with the enchanted hammer-wielding Beta Ray Bill, who trapped her in an adjacent parallel dimension.
Terrax
Terrax was already an immensely powerful Marvel cosmic villain before becoming a herald of Galactus. Possessing the ability to animate stone, he subjugated the people of his homeworld, ruling over them as a tyrannical dictator. Galactus, at this point, had become dissatisfied with the nobility shown by previous heralds and sought a more ruthless and uncompromising candidate. Terrax fit the bill, and after being imbued with the power cosmic, his stone controlling powers were massively increased, enabling the villain to animate entire 100-mile-wide planets.
As Galactus had expected, the immoral Terrax had no qualms leading the annihilator to worlds teeming with life. Unfortunately, his ruthless ambition also left little room for loyalty, and Terrax began secretly conquering worlds for himself, only continuing to serve Galactus out of fear. When Terrax finally turned against his master, Galactus stripped him of his cosmic powers and abandoned him on earth.
Morg
A ruthless and bloodthirsty court executioner, Morg volunteered to serve as a herald of Galactus, even after the cosmic being consumed his homeworld. As with all heralds, Morg was granted the power cosmic. He then found the ancient "well of life" and used its energies to further increase his powers.
Unwaveringly loyal, Morg proved incredibly effective as a herald, leading to the destruction of dozens of inhabited worlds. Recognizing Morg's increasingly devastating cosmic threat, the Silver Surfer assembled a team of previous heralds to battle him, including Firelord, Nova, and the rebuilt Air-Walker android. While the group succeeded in defeating Galactus' newest servant, their victory came at a price, with Frankie Raye perishing to Morg in combat.
The Fallen One
The ancient Fallen One was Galactus' very first attempt at conscripting a herald to serve him. Unlike the others, the Fallen One has the unique distinction of being the only of Galactus' heralds to be powered by dark energy, rather than the power cosmic.
This allowed the immensely powerful being to manipulate the very binding fabric of the universe, making him a threat to even Galactus himself. When the Fallen One proved to be unnecessarily cruel in his actions, Galactus banished his first herald to a realm between dimensions. Despite this, he has periodically returned to attempt revenge upon his former master and has come close to succeeding on a handful of occasions.