Only known surviving member of the Soldato Battalion, a series of combat cyborgs developed by the Red Planet's leader, Abel. They would function as commanders of the J-Ark fleet, and perform Fusion with them to fight the Z-Master. Abel's extensive preparations would not be enough, however, as the failure to unite Soldato, Alma bioweapon, living computer, and J-Ark battleship into a cohesive team would lead to the failure of the world's defenses and, eventually, the planet's mechanization. As a Cyborg, Soldato J has impressive strength and speed. The green scarf attached to his armor can extend and harden into a pair of wings for flight, and the left gauntlet contains a Radiant Ripper, an energy sword. While normally used with both hands, the Radiant Ripper can be used while still attached to the gauntlet, as seen in FINAL.

As one of the two surviving members of the Battalion, Soldato J 002 fought alone (his J-Ark's main computer—Tomoro 0117—had been lost to Zonder infection and his J-Ark was sent into space to protect its infant Alma onboard), going so far as to confront Arm Primeval, one of the leaders behind the offensive on his world. J would confront Arm alone, and barely lost their confrontation, forced to flee into the wasteland that was now his planet. He was subsequently captured by his own living computer—transformed into the Zonderian Pinchernone—and converted into the Zonderian Pizza, the memory of his proud past sealed away.

As Pizza, he and Pinchernone would accompany the Zonderian "terminal" program Pasder to the "Blue Planet"—Earth—with the order to infect all of humanity with Zonder Metal. Even as a Zonderian, however, Pizza would have brief flashes of the time before he was mechanized. He became a great rival of the GGG Mobile Unit commander Guy Shishioh; through his duels with Guy, his old pride began to recover, along with his a sense of his old purpose. In a burst of defiance, he protected his rival from a direct attack from Pasder, leaving him critically wounded. He would be saved by his Arma, who had landed on Earth and had adopted the identity of Ikumi Kaidou. Kaidou performed Purification on Pizza and Pinchernone, restoring to them their true forms and memories.

Following his restoration, Soldato J would dedicate himself to his original mission once again: to destroy the Z-Master. To this end he would re-unite with his team in his J-Ark (crashed within Mt. Aso in Kyūshū, Japan) and wait for the arrival of the 31 Machine Primevals. Upon the Primevals' arrival on Earth, he showed just how powerful the original Red Planet fleet could have been had it been properly organized. They began an independent mission to destroy the Primevals—ignoring the battles of the Gutsy Galaxy Guard, going over their heads and even clashing with them head-on. As J and GGG realized they had a common goal, however, they began to grudgingly help each other to defeat the 31 Primevals.

During this time, J would also confront and destroy the other surviving member of the Soldato Battalion: Soldato J #019, who had since pledged his loyalty to the Z-Master and had his J-Jewel replaced with a Zonder Crystal (this story was told in the manga serial "Wings of Light and Darkness").

In the final battle with the Z-Master, J and Kaidou entered Heart Primeval and set "THE POWER" in the J-Ark to overload, creating a cascade reaction that would destroy the Z-Master from within (also critically damaging King J-Der in the process). Judging this to be a fair trade, J and his team were fully willing to sacrifice themselves in order to end the Zonder threat once and for all. It was revealed that the J-Ark survived the final fight, falling into a wormhole generated by "THE POWER" and emerging at a point 90 million light-years outside of the universe. There, the J-Ark began its slow restoration process. From their unique perspective, Tomoro 0117 determined that the universe was contracting in size; tracking down the source of the contraction, the J-Ark reappeared within Earth's solar system in orbit of Jupiter, where they found an exhausted Mamoru Amami and a mysterious device called the Pas-Q Machine. As Mamoru asked Kaidou to take this device to Earth, Pia Decem of the 11 Planetary Masters of Sol attacked; Kaidou returned to Earth with the Machine, but J retreated to the Tri-Star System with Mamoru.

Soldato-J and his J-Ark covered Mamoru's retreat to the G-Crystal but were themselves captured by the other Masters of Sol and imprisoned on the repli-Earth created by the Pas-Q Machine (at the island of Mont Saint Michel). They would thereafter be freed by Renais-Kerdif Shishioh and Mikoto Utsugi, only to face Palus Abel—the 11 Masters' leader whose program was based on Abel herself. She would soon after reveal that she had captured Ikumi Kaidou and was using him as the living computer core of Pia Decem Pit; unable to attack Pia Decem directly because of this, King J-Der was soon forced into a fight with a mind-controlled Guy Shishioh. The resulting clash between J-Quath and Goldion Hammer left both weapons destroyed. Palus Abel routed remote commands through Kaidou to shut down the J-Ark and Soldato J's own J-Jewel; Pia Decem and Pillnus captured him and Renais Kerdif-Shishioh soon after, though they would escape through sheer accident—bringing Renais' G-Stone into proximity with Soldato-J's J-Jewel restored them both, activating their Hyper Modes. It is at this point that J's helmet is partially broken, allowing the only view of his eyes in the series. With the subsequently rectivated J-Ark, they proceeded to confront Palus Abel aboard the Pia Decem Pit.

Despite many fans using the translation "Soldat", the correct (and official) translation is Soldato. Soldato is an Italian word(like Arma and Pizza) and means "Soldier". Soldat, though, does mean "Soldier" in several languages as well, including Swedish

Soldato J appears to be a homage to Cyborg 002 of Cyborg 009, who together share a similar design, common number, personality, and fondness for flying. Sunrise and Toei Animation collaborated on a Cyborg 009 adaption in the late 1970's, the era of which GaoGaiGar attempts to thematically honor.