The Legion of Darkness was formed years ago after the Hero Factory just became a major presence in the galaxy. Black Phantom recruited fellow villains Thornraxx, Speeda Demon, Jawblade, & Splitface at a repair shop used by the criminals, he informed them about his plan to take down the newly-formed Hero Factory that was endangering the criminal activities of the villains across the galaxy. Interested, the four villains joined Black Phantom's ranks & planned an attack upon one of Akiyama Makuro's transport ships that carried 24 recently created industrial robots from a Makuro Industries plant under Black Phantom's orders. After Thornraxx took control of the cargo ship & landed behind a hill, Black Phantom had 23 of the robots reprogrammed to wander around the galaxy without any purpose, while the last robot was reprogrammed to work as Black Phantom's assistance, going under the name XT4.
XT4 was used to infiltrate Hero Factory & steal it's data, & to break Voltix & Toxic Reapa out of prison on Asteroid J-54. Splitface & Speeda Demon piloted a hijacked ore freighter to the Asteroid, & Black Phantom a Drop Ship. When the Alpha 1 Team sans Thresher arrived in chase of XT4, XT4 saved Voltix & Toxic Reapa & initiated a mass prison break. As Von Ness let them escape, Splitface rigged the freighter's engines to blow & went with Black Phantom. All the Legion escaped & Preston Stormer & Jimi Stringer were nearly killed in the incident. The Hero Factory was so rattled Akiyama Makuro's 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, Jawblade taking down the security systems, XT4 & Splitface going to the power core. After ejecting Thornraxx, Toxic Reapa piloted his ship with Speeda Demon & Voltix to the Assembly Tower. There they fought Thresher while Splitface & XT4 dueled Stormer. Thresher was defeated, & 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 & get arrested.
Four of the villains: Speeda Demon, Jawblade, Voltix, & Black Phantom later escaped, though Speeda & Jawblade were recaptured by William Furno. Furno & Rocka captured Voltix which caused every villain including the former legion members to escape.