Founded by Menniker, son of Dimitri, the Dark Legion was originally made up of a group of disgruntled Echidnas opposed to the Brotherhood of Guardians and their ban on excess technology. After their first battle, the Legion was banished to the Twilight Zone, a realm where time passed differently than on Mobius proper, resulting in four Mobian generations to every single Dark Legion one. However, they would later return over the years to battle the Guardians and strike at the Echidna people. Overall, the primary goal of the Legion has been to first dominate Angel Island, and then the rest of Mobius.
The main identifying trait in the ranks of the Legion is their devotion to technology. These echidnas are so obsessed with mechanics that they even replace parts of their own bodies with machine implants. They also believe themselves superior to other species.
First appearing as a terrorist organization, the Legion launched devastating strikes against Echidnaopolis. After failing to defeat the Guardian Steppenwolf, they were trapped in the Twilight Zone, only to reemerge for a second strike which likewise failed, despite conspiring with the Overlanders. Later, they launched a mass assault on Echidnaopolis, resulting in the accidental switching of Tobor and Moritori Rex.
When the barrier between Mobius proper and the Twilight Zone was erased by the Ultimate Annihilator, the Dark Legion began a long campaign against Echidnaopolis. This involved several incidents of open warfare, kidnappings, and even an attempt to grab at political power. Later on, however, Dimitri apparently wished to reunify the Echidna people, and attempted to establish peace between the Legion and the people of Echidnaopolis.
Dimitri's efforts appear to have been somewhat successful, as the Dark Legion was the resistance force on Angel Island against the Eggman Empire backed Dingos. However it was revealed that since they worked together with the Freedom Fighers and Chaotix against the combined threat, the Legion had splintered into two groups: the Frost Legion, controlled by a brain-addled Constable Remington, and the Flame Legion, still under the command of Lien-Da. Both groups then became entangled in a civil war with each other, which only stopped when former Dark Legion member Dr. Finitevus asked for a truce, allegedly because he planned to use the Master Emerald to grant a reunited Legion the power to deal with the threat of Dr. Eggman and save the rapidly-dwindling echidna people.
Once it became clear that Dr. Finitevus would not honor his promises and had instead granted Enerjak's power to a brainwashed Knuckles the Echidna in a bid to "cleanse" the world, the warring factions put aside their differences in order to deal with the new threat. When the Legion tried to defeat him using conventional weapons, he restored them all to normal Echidna forms and transported most of them to Albion, with the exception of those who, like Lien-Da, were repulsed by the idea of losing their bionic enhancements. Knowing that her diminished forces could not return to power alone, she made a deal with Dr. Eggman, asking for his aid in replacing their bionics in exchange for the Dark Legion's servitude. Robotnik agreed, making them part of the Eggman empire as his "Dark Egg Legion", but revealed to Lien-Da that she would not be Grandmaster; that role would be filled by Dimitri, who had already approached Robotnik in hopes of destroying Enerjak.