Serving as a captain in the Xandarian Nova Corps with his friend, Pyreus Kril, Gabriel was abducted and transformed into Air-Walker by the world devouring Galactus, becoming his herald; Kril would later become Galactus' herald, Firelord. Air-Walker took Galactus to countless worlds, and the two became close. Gabriel actually loved Galactus as a father, and Galactus was also very fond of his herald, telling him endless stories of his travels throughout the cosmos. When the Ovoids, an alien race determined to rid the universe of Galactus' threat, attacked, Air-Walker sacrificed himself to defend his master. Attempting to save his herald, Galactus transferred Gabriel's life force into a highly advanced robotic shell, but the android had no memory of his previous life and was lacking something his Xandarian counterpart had. Galactus had Air-Walker travel to Earth to draw out his previous herald, the Silver Surfer, so Galactus could take him as his herald once more.
Mistakenly assumed to be the Archangel Gabriel upon first arriving on Earth, Air-Walker sent the world into chaos after sounding his Trumpet of Gabriel and proclaiming the imminent destruction of mankind. The Fantastic Four attempted to peacefully reason with him, but when Gabriel refused to listen, they resorted to force. Turning the city of New York against the heroes by telling the masses the way to avert their destruction was by killing the heroes, Air-Walker only delayed the inevitable confrontation as the Fantastic Four evaded angry mobs. Stronger than the Thing, unfazed by Human Torch's fire (including a near-nova flame), and unimpeded by Mister Fantastic's gadgets, Air-Walker appeared unstoppable until the Surfer witnessed the Fantastic Four's plight. The Surfer matched Gabriel's power and determination, but was paused when Gabriel told him of Galactus' intentions. The Surfer refused to return as herald, and Gabriel enveloped him in his Cape of Destiny, boasting no one had the power to escape the cape's grip. The Surfer did escape and destroyed the cape doing so. Air-Walker declared the cape was his source of power and life as he plummeted to the ground and was deactivated on impact.
Gabriel's body was recovered by the Machinesmith, and his self-repair systems were activated. Once resurrected, he was spotted leaving the Machinesmith’s lair by a young child, Kevin. Remembering his past encounter with the Silver Surfer and the Fantastic Four, he went to the Baxter Building to ask his enemies what transpired since he was offline. Taking Kevin with him, hoping the boy could enlighten him about his new environment, the Fantastic Four believed Kevin was a hostage and wanted to rescue him, but Air-Walker used his power to seal them within their headquarters. Discovering Galactus left Earth and abandoned him, Gabriel was enraged at being discarded and having his mind placed within an android shell without his consent. He created a cosmic storm, hoping to renew his conflict with the Surfer, but it was Thor who confronted Air-Walker after ending the tempest. Also thinking the boy to be a prisoner, Thor attacked but was defeated when Air-Walker smothered him within the Cape of Destiny and wrestled his enchanted hammer, Mjolnir, away from him, rendering Thor unconscious with it. Kevin believed Gabriel was a noble entity and inspired him to rethink his actions. Gabriel dropped Thor to the ground, but when he recovered, Thor hurled Mjolnir through the robot's chest, deactivating him. Firelord saw the televised battle and went to aid his old friend, attacking Thor. Calming himself, Firelord told Thor the tale of Gabriel Lan, and afterward buried Gabriel on an asteroid in Xandar’s solar system.
Sometime later, Galactus found a herald in the murderous Morg, and the Silver Surfer voiced his concerns. Galactus dismissed his former herald and Morg defeated the Surfer in combat. The Silver Surfer, and former herald Nova, recruited all former Heralds of Galactus, including a newly reactivated Air-Walker, to oppose Morg. After an epic battle which left Nova dead and Morg defeated, Air-Walker and Firelord agreed to act as heralds to Galactus, and Firelord hoped to rekindle Gabriel’s humanity. Both were eventually replaced by Red Shift. When the forces of Annihilus cut a path of destruction across the universe, Air-Walker, like all the former heralds, was hunted. He was about to be overrun, but the Surfer helped him hold their opponents at bay. However, Air-Walker's wounds were too severe, and his robotic form could not repair itself. Gabriel expired and the Surfer ensured his remains could not be tainted by Annihlus by causing an explosion that presumably destroyed his robotic form completely.
