An alien with the ability to generate flames from the right hand and extreme cold from the left. Mercurio is a native of the planet Gramos, a world threatened with extinction when a gravitational distortion blocks out all sunlight. In a bid to save Gramos, Mercurio was chosen to project his consciousness across the galaxy to Earth, where he takes control of a wealthy landlord and uses his resources to build a device to siphon off Earth's electro-magnetic field. Mercurio also detects strange energies coming from the offices of Dr. Donald Blake, the alter-ego of the Thunder God Thor. Witnessing a transformation from Blake to Thor, Mercurio siphons off some of the magical energy in attempt to transport his body across space to Earth. The process is only partially successful as the left side of Mercurio's body is turned blue-black and his normal fire-generating ability is reverted to ice (on the left side only). Mercurio then battles Thor but is quickly defeated.
Several weeks after returning to Gramos, Mercurio leads an army to find the God Jewel, a gem containing enough energy to sustain Gramos forever. The God Jewel, however, proves to be sentient and evolves into a humanoid form called Xorr, and is capable of sucking the life energy from any source. Coincidentally, Thor and several allies are also seeking the God Jewel as it has imprisoned two Asgardian goddesses. With Thor's help Xorr is defeated, and Mercurio retrieves several fragments of the God Jewel for use on Gramos.
Although Gramos is saved, Mercurio develops a desire to conquer, and attempts to trick Captain Marvel into visiting Gramos and building the Omni-Wave Projector - a device capable of emitting energies on a galaxy-wide scale. Captain Marvel's cosmic awareness, however, warns him of the trap and after defeating Mercurio he returns to Earth.
Mercurio was most recently seen as a prisoner on the laboratory-world of the Stranger.