The Legion of Darkness was formed years ago after the Hero Factory became a major presence in the galaxy. Black Phantom recruited fellow villains Thornraxx, Speeda Demon, Jawblade and Splitface at a robot repair shop used by the criminals, and informed them about his plan to take down the newly-formed Hero Factory that was endangering the criminal activities of villains across the galaxy. Interested, the four villains joined Black Phantom's ranks and planned an attack upon one of Akiyama Makuro's transport ships, which carried twenty-four recently created industrial robots from a Makuro Industries plant, under Black Phantom's orders. After Thornraxx took control of the cargo ship and landed behind a hill, Black Phantom had twenty-three of the robots reprogrammed to wander around the galaxy without any purpose, while the last robot was reprogrammed to work as Black Phantom's assistant, going under the name XT4.
XT4 was used to infiltrate Hero Factory and steal it's data, and to break Voltix and Toxic Reapa out of prison on Asteroid J-54. Splitface and Speeda Demon then piloted a hijacked ore freighter to the Asteroid, and Black Phantom arrived in a Drop Ship. When the Alpha 1 Team-sans Thresher]-arrived in chase of XT4, XT4 saved Voltix and Toxic Reapa and initiated a mass prison break. As Von Ness let them escape, Splitface rigged the freighter's engines to blow and went with Black Phantom. All the Legion members escaped, and Preston Stormer and Jimi Stringer were nearly killed in the incident. The Heroes was so rattled that Akiyama Makuro closed Hero Factory. Black Phantom convinced the villains they would take Hero Factory, but in actuality he wanted them captured leaving him the destroyer of Hero Factory without any competition. The villains arrived, while Jawblade taking down the security systems while XT4 and Splitface went to the power core. After ejecting Thornraxx, Toxic Reapa piloted his ship with Speeda Demon and Voltix to the Assembly Tower. There they fought Thresher while Splitface and XT4 dueled Stormer. Thresher was defeated, and Black Phantom defeated Stormer until the rest of Alpha 1 arrived. In a chaotic battle Black Phantom's treachery was exposed by Stormer, causing the Legion to disband and get arrested.
Four of the villains: Speeda Demon, Jawblade, Voltix and Black Phantom later escaped, though Speeda and Jawblade were recaptured by William Furno. Furno and Rocka captured Voltix which caused every villain including the former legion members to escape.