The Reducing Ray was built by Doctor Doom. Doom intended to utilize the shrinking ray to reduce the Fantastic Four to nothingness. During battle with the Fantastic Four, an errant blast from Doom's gauntlet blaster struck the reducing ray's control panel, causing it to activate while he was standing directly in front of it, reducing him to nothingness. This transported him to the microworld of Sub-Atomica.
In Sub-Atomica, Doom quickly used his technological genius to assume control of the Microworld and developed a new version of his Reducing Ray, which he used to toy with the Fantastic Four. The Fantastic Four, aided by Ant-Man, soon journeyed to Sub-Atomica and battled Doom, who used his recently-developed Enlarger Ray to return to Earth.
This pistol-like device projected a ray that may have reduced the physical size of whatever it may have struck.
- Doctor Doom may have utilized Reed Richard's notes on Henry Pym's Reducing formula in order to develop this device.
- A working version of the Reducing Ray was left in possesson of Pearla and her father in Sub-Atomica, at the end of Fantastic Four #16; Doom had built one new unit after reaching Sub-Atomica. Machines of Doom states that the original unit was still in posession of the Fantastic Four.
- Doctor Doom built the Reducing Ray while inhabiting the body of Mister Fantastic.
- As the effects of the Reducing Ray are permanent, Doom was forced to develop a different machine, the Enlarger Ray, to recover his size.