Nebulon is an Ul'lula'n, an extraterrestrial race with six-tentacles and fins that breathe water and measure about 10 feet (3.0 m) in length. He was one of a number of Ul'lula'ns dispatched to find worlds with mineral resources that they had depleted on their own home-world of Ul'ula in the Ul system, in the Milky Way galaxy. He took on a glistening form as a golden humanoid in an attempt to blend with Earth's human population. Nebulon happened upon the evil Hyperion from the Squadron Sinister who was trapped in outer space, and rescued him. Hyperion led the alien back to Earth to let him have it. Nebulon helped Hyperion gather the other Squadron Sinister members to build a laser cannon that would melt the polar ice caps and flood the planet, making it perfectly suitable to the Ul'lula'ns.^[1]

Nighthawk, a former Squadron Sinister member, had been coerced into helping with this plan. He contacted the Defenders, who traveled to the North Pole and fought the Squadron Sinister. During the course of the battle, Nebulon used up so much of his energy that became unable to control his humanoid form and reverted to his monstrous form; Nighthawk took advantage of the confusion this caused among Nebulon's allies and turned the laser cannon against Nebulon, causing him to seemingly implode.^[2]

In reality, Nebulon retreated to another dimension called Zaar, inhabited by the Ludberdites. Nebulon adopted their philosophy of improving the lives of "lesser" beings, and returned to Earth to save its people from themselves. In the guise of "Mr. Nebul," he began what he called the Celestial Mind Control movement that promised to unleash the powers inside the human mind, but instead actually robbed people of their free will.^[3] Nebulon recruited the Porcupine, the original Eel, and a Plantman simulacrum as his agents.^[4] The Defenders became aware of this movement and tried to stop him. However, he exiled the Defenders by sending them to another dimension.^[5] Concurrent with Nebulon's movement, the Headmen were attempting a similar movement. Nebulon engaged in battle with the Defenders and the Headmen. When the Defenders exposed the Headmen's political machinations, they managed to convince Nebulon of the futility of his goal, and Doctor Strange persuaded him to leave Earth.^[6]

When the Ul'lula'n government learned of Nebulon's activities, it tried and convicted him for treason. Nebulon escaped into Earth's ocean and took the form of the deceased Lady Dorma. He convinced the Atlanteans that she had survived, and used her popularity to convince them to make an attack on London, but the Defenders uncovered his latest deception. Not long after that, an Ul'lula'n ship appeared to take custody of Nebulon.^[7] The authorities stripped much of his power from him, fixing him in his humanoid form, and exiling him on Earth. He was ordered to do the honorable thing and commit suicide, but refused. Nebulon's wife, Supernalia, learned of his dishonor and went to Earth to convince him to do the right thing. Nebulon was planning to use his technology to siphon power from the Avengers and restore his powers. Supernalia convinced the Defenders to help her, and the Defenders and Avengers were manipulated into fighting each other on the behalf of the two Ul'lula'ns. Supernalia realized that her own actions violated their people's ethics, and threw herself into the energy-draining ray; Nebulon tried to save her but fell into the ray himself. As Nebulon died from the bombardment by the energy-draining Ennui-ray, he believed he was finally acting in an honorable manner. The Avengers and Defenders then buried the two aliens in the place where they died, under the snow of the Himalayan Mountains.^[8]

Nebulon's powers are a result of biospheric energy and his alien physiology. He has superhuman strength, durability, and reflexes. Nebulon had the ability to manipulate energy to use it for various effects, such as creating spheres, shields, or bolts of energy, teleportation anywhere on the surface of a planet or between dimensions, and shape-shifting. Nebulon's powers were dependent on biospheric energy generated by planets. If he were deprived of contact with a planetary biosphere long enough, his power level would be reduced to that of a normal human being. In his true form, Nebulon appears as a 10-foot (3.0 m) long gigantic six-tentacled cephalopod.

Nebulon possessed a gifted intellect and has extensive knowledge of existential philosophy.

• Nebulon at The Appendix to the Handbook of the Marvel Universe
• http://en.marveldatabase.com/Nebulon_%28Earth-616%29