Shadow
Arch enemy of the Galactic Patrol and Mighty Orbots, Shadow is a sinister organization led by Umbra, which intends to take over the galaxy. Whether Shadow is a crime syndicate or a sovereign foreign government is not clear, but they do seem to have vast resources, as well as spies and agents placed nearly everywhere. Hamstrung in their attempts at galactic domination by the forces of the United Panets, Shadow must resort to terrorism and covert operations, in which they are continually thwarted by Mighty Orbots.

The Shadow Star
The headquarters of Shadow is the mysterious and deadly Shadow Star, which is essentially a Dyson Sphere, or a shell around a star that can capture all of the available light. The weaponry and defensive systems of the Shadow Star are so ominous that a direct assault by Galactic Patrol forces is considered to be out of the question. The Shadow Star can generate so much power that it is able to move under Umbra's direction, and any sector of space it occupies will be totally under Shadow control.

Umbra
The master of Shadow, Umbra is a massive, powerful biological computer bent on galactic domination. Self-described as a "cyborg," Umbra's origins and true nature are unknown. In his cavernous reception hall deep within the Shadow Fortress, Umbra appears as a macabre, disembodied five-eyed face in a fluid tank. Whatever the biological element of Umbra might be, he is mostly a mechanical computer, serving as the central nervous system of the Shadow Fortress, and as the brains of Shadow itself. Umbra's memory banks stretch for miles within the Fortress. Umbra has become obsessed with the destruction of the Galactic Patrol, specifically Mighty Orbots. He has placed all of the resources of Shadow into the sole task of destroying Mighty Orbots, and each episode he has a new plot to accomplish this end.

(Spoiler Alert!): Defeated time after time, Umbra ultimately resorted to luring the Orbots to the Shadow Star in a final attempt to destroy them. This battle ultimately resulted in the destruction of the Shadow Star, but as Umbra's image boiled away into space, he vowed that he would return to final victory. So, it is fairly certain that somewhere, in some form, Umbra is still alive.
(Unfortunately, the series was canceled, eliminating any chance for Umbra to keep his promise.)

The Shadow Fortress
Floating on the surface of the inner shell of the Shadow Star is the Shadow Fortress, a mammoth military installation the size of a continent. The Fortress is essentially a mechanical body for Umbra's formidable brain, complete with internal defense mechanisms.

Shadow Agents
Umbra's agents are a mishmash of humans, robots, and various aliens, so Shadow appears to be more of a terrorist organization than a sovereign nation. Shadow agents seem to be infiltrated nearly everywhere; if something strange is going on, you can bet there's a Shadow agent somewhere about. They even go so far as to take over entire organizations, including circuses, mining companies, and even prison facilities.

Dragos & Drax (Magnetic Menace)
A pair of robotic agents posing as rock superstars. They can use their music both to brainwash listeners as well as to create a fearsome magnetic-field entity. They were captured by Dia attempting to escape the Moon after creating the monster.

Doctor Phoenix (The Phoenix Factor)
A cyborg scientist from ancient Earth, Doctor Phoenix was awakened and enlisted by Umbra to continue work on his mechanical virus, Mechanogen. Always uncomfortable with Umbra's motives, Phoenix turned on Shadow and helped Rob find an antidote. However, he still went to trial for his crimes.

Drennan (Operation Eclipse)
A school friend of Rondu's (and of the same elfin race), Drennan's mental, physical and psionic powers are impressive. Unfortunately, he became so jealous of Rondu's success that he defected to Shadow, allowing Umbra to cripple the United Planets fleet at Centris. This ultimately led to a mental duel between Drennan and Rondu, which Rondu won.

Kattron (The Wish World)
A generic Shadow warrior in gigantic samurai-esque armor, Kattron was defeated by Mighty Orbots in the Emerald Nebula. Bo heated his armor to the point where it fused into a single piece, and the Orbots merely hauled him off to prison. Kattron's primary weapon was the "Multi-Beam," projected from a shield-like device.

Plasmus (The Wish World)
One of Umbra's most formidable agents, Plasmus is a shape-shifter with the ability to fly and to absorb energy. Plasmus was successful in tricking Ohno into becoming human, and discovered the secret of the Orbots' true identities. So, the Orbots tossed him into a hyper-warp, and he's currently lost somewhere on the other side of the galaxy.

Torkus (Leviathan)
A member of an aquatic race, Torkus ran the entire mining operation on Aquarius. The whole thing was just a front to cover the company's real goal: the discovery of the Solar Sphere. His plans were discovered and thwarted by Mighty Orbots, and he was captured before he could escape Aquarious.

The Ringmaster (The Cosmic Circus)
The Ringmaster's entire circus works for Shadow. They were sent to Earth to capture and duplicate key Galactic Patrol officers in an attempt to disable Earth's computer-controlled defense system. As usual, Ringmaster and his cohorts were captured by Mighty Orbots.

Draconis (Devil's Asteroid)
An agent who managed not only to infiltrate the prison planet of Devil's Asteroid, but also to bring it almost totally under Shadow control. After Umbra's Orbot-clone Tobor has successfully framed Mighty Orbots for assault, Draconis delighted in torturing the Orbots in Devil's Asteroid.

Mentalis (Trapped on the Prehistoric Planet)
The most intelligent of Umbra's agents, Mentalis used his helmet to mind-control the various creatures of Evilon, and send them after Mighty Orbots. Mentalis was captured by Dia, but not before he sent a huge asteroid hurtling towards Earth.

Nordak (Trapped on the Prehistoric Planet)
Another generic Shadow monster, whose defeat by Mighty Orbots was shown on television, much to Umbra's chagrin.

Darra (Jewel of Targon)
Sent to Targon to place a trap for the Orbots, Darra's reward from Umbra was to be left there to die. Not surprisingly, Darra made a deal with the Orbots in return for transport off Targon.

Werag (Invasion of the Shadow Star)
Umbra's chief scientist, Werag developed the ultimate weapon, the Sun Smasher. Capable of destroying entire solar systems from extreme range, this weapon triggered the invasion and ultimate destruction of the Shadow Star. Werag is presumed to have perished along with the Shadow Star.