Nucleon is a Decepticon Titan Master from the Titans Return portion of the Generation 1 continuity family.

Mini Megs

Nucleon is with Galvatron, and has the ability to enhance the larger Decepticon leader's powers by forming his head. While the power he grants Galvatron is formidable, it's also fairly unstable and runs the chance of making the Decepticon more than a little haywire.^[1]

He bears a remarkable similarity to Megatron.

Fiction

Titans Return marketing material

Nucleon was presumably present as his larger partner's head when Galvatron declared that the Decepticons would possess the power of the Titan Masters for themselves. Titans Return: The Power of the Titan Masters

Beast Wars: Uprising

Nucleon was once a simple Cyberdroid, an inhabitant of the Cybertronian colony world of Rebirth. As his planet chafed under the crumbling oligarchy of the Optimus, his Conjunx Kari was arrested for speaking out against the corrupt rulers. A grief-stricken Nucleon joined up with the Malignus faction. When Galvatron arrived on the planet, Nucleon was inspired by the Decepticon rhetoric and joined up, spearheading the development of the Powermaster process. He, Clench, and Doomshot all binary-bonded themselves to Galvatron, and the foursome crushed the Optimus leadership underfoot. Nucleon became an accomplice in Galvatron's future adventures, including the disastrous Great Push which saw the Decepticon advance utterly routed at the hands of the Human Confederacy. Nucleon was present to watch the trial of Galvatron that ended in the latter's execution by vivisection. Nucleon and his fellow Cyberdroids served out indefinite prison sentences on Cybertron. A Brush With Infamy–Prologue Eventually, a regime change led to Nucleon and the others being released from custody. Micro-Aggressions Not All Megatrons

Centuries later, a bitter and impoverished Nucleon, now little more than a drifter, was hanging out in Fort Scyk as he watched the Maximals and Predacons and mused about the dire state of the universe. His philosophizing was interrupted when a mysterious stranger — a doppelgänger of the original Galvatron — told Nucleon that he was "getting the band back together". Not All Megatrons The new Galvatron reunited Nucleon with Krunix and Doomshot, and together the trio of Cyberdroids were able to procure a Darksyder Beast Pod for their master, which he used to grant himself a beast mode. Unfortunately, the upgrade also meant that he no longer required his old Cyberdroid partners, and when the Vehicon Apocalypse swept Cybertron the three nervous Cyberdroids proved themselves almost entirely useless in the face of the relentless Vehicon hordes. Disgusted, Galvatron ordered them to procure some Vehicon specimens, so that he could figure out how these new Transformers worked. Derailment

Nucleon's engineering prowess came in handy as the quartet studied the physiologies of the Vehicons in the Rad Zone, and before long Galvatron had three new reverse-engineered Vehicon generals under his command. Unfortunately, that also meant that the Cyberdroids had outlived their usefulness and Galvatron disposed of his old partners. The Inexorable March

2019 IDW continuity

A normal-sized Transformer, Nucleon attended a skitter race at Swindle's. Swindle's

Toys

Titans Return

• Nucleon & Galvatron (Voyager Class, 2016)

• Known designers: John Warden (Hasbro), Emiliano Santalucia (concept artist), Marcelo Matere (packaging artist)

Nucleon was released, along with his larger partner Galvatron, as part of the first wave of Titans Return Voyager Class figures. He can transform into Galvatron's head for robot mode, which is also compatible with any other Titans Return Deluxe-or-larger figure. Then again, Galvatron can have any body he wants, even some other bots from other continuities.

When he was unveiled, Nucleon's body was painted entirely silver and his head mode was painted purple, though the final product leaves him almost entirely without paint applications.

it is important to note that some samples of the figure have issues with how the Titan Master connects. Your mileage may vary, but some must be attached with Nucleon's head twisted backwards (with Nucleon and Galvatron both looking in the same direction), or else one risks Nucleon's head breaking off inside Galvatron's collar assembly.

Nucleon's mold was also used in Japan as Megatron, the small Headmaster stage of Legends Galvatron, and as Megaligator.

• More information on Nucleon (with Galvatron) at TFU.info

References