History
Doctor Doom developed this device[1] which prevented other people from attacking him directly.[1][2] Specifically, the Ray broadcasted an invisible area in Doom's immediate vicinity that psychically affected anyone trying to attack Doom at point-blank range.[1] Even the strong-willed Thing failed to attack Doom directly[2] although theoretically some people would be able to overcome the device's effect. The effect lasted up to ten hours[1] but it required some time to affect a subject. During this time, the subject was to be distracted.[2]
The Inhibitor Ray, while amazingly advanced[1] and discreet enough to be hidden in Doctor Doom's Armor[1][2][3] -indeed its appearance is unknown- was nonetheless fragile if directly attacked, and was useless against non-organic enemies such as robots.[1]
The Inhibitor Ray was used against the Fantastic Four as a part of Doom's so-called "Plan Epsilon". At that point, Doom had been deposed as ruler of Latveria by King Zorba and Doom himself had been trapped outside his body but Doom's loyal Doombots started Doom's pre-defined Plan Epsilon to restore him to his body, then to his throne. To do so, the Doombots summoned the Fantastic Four to the Latverian Embassy in New York City. The Fantastic Four were separated from each other, and each of the heroes faced a Doombot that pretended to be Doom himself. The robot was easily destroyed by its opponent, but the real goal was to keep the hero occupied until the Inhibitor Ray could do its effect. Only then, the recently-restored Doom appeared in front of the heroes. The Thing tried to attack Doom, only to discover he could not, and Doom explained the device.[2] The Fantastic Four were Doom's enemies and he was in a good position to destroy them thanks to the Inhibitor Ray, but instead he recruited them as allies to recover Latveria. After succeeding at that, Doom graciously let them leave his domains, because attacking them at that moment and with the Inhibitor's Ray advantage was too petty for Doom.[3]