Harley was orphaned at age 11 and grew up as part of a gang that lived in the East End of London. They lived by foraging and stealing what they needed to survive. Her incredibly foul language earned her the nick-name Motormouth. When she was seventeen Harley was discovered by Laarson, an agent of Mys-Tech, the shadowy organisation. Harley was a candidate for his M.O.P.E.D (Mind Operated PErsonal Dematerialization) technology. This allowed people to jump between alternate realities. The MOPED unit was disguised as the pair of training shoes, which Harley found and tried on.
At the same time, Laarson was being executed by Mys-Tech's Techno-Wizards and agents were sent to find the MOPED units. In order to save her and the units, Laarson's subordinates activated the technology and sent her to another universe.
While still on the run from Mys-Tech, Harley was sent to a future where the world was covered in shopping malls. It was here she purchased a Soni-Muta 500 Unit, a microchip that allowed her to mentally tune into any radio station she wanted. This would later give her her sonic scream. Harley returned to her own universe and was capture and put to work by Mys-Tech. She escaped after a mission to Tokyo, Japan. She had to make a random jump and ended up on a planet named Tekron. Killpower, an agent of Mys-Tech was sent to find her.
Unable to escape him, Harley reasoned with the agent instead. Mentally little more than a small child, Killpower was intrigued by Harley and has since been her partner. Harley was then badly injured on Tekron when a stray bullet hit her in the throat, Killpower used her Soni-Muta 500 and the MOPED technology to cure her. This not only gave her the aforementioned sonic scream, she could now travel between universes without the aid of technology. Killpower joined her in fleeing from Mys-Tech.
Death's Head was hired by Mys-Tech to retrieve Killpower; while the two fought, Motormouth and Tuck, Death's Head partner, went on a shopping spree on an alien planet. Motormouth and Killpower later planned an attack on Tyburn, a powerful Mys-Tech agent. Harley was able to steal their MOPED unit and nuetralize the tracking devices Mys-Tech had implanted in the duo. Tyburn survived the attack.
When Death's Head slew the Techno-Wizards, the entire world became threatened. Motormoth was one of the six surrogates who repaired the damage done and restored the wizards. The others who took part in this were mostly powerful mystics such as Doctor Strange; Harley was part of it 'because they needed six' and had little part in the actual events. Killpower had been an essential part in the fight against Mys-Tech but did not remember it due to the nature of the events.
Both Motormouth and Killpower were recruited by the Time Guardian to help stop a war on the planet Eopia. The war had been caused by Tyburn and Mys-Tech agents had infiltrated both sides of the war. Motormouth was instrumental in stopping a powerful Mys-Tech agent called Collapser who had captured Killpower, her extra-sensory vision allowed her to see microfractures in his torso which in turn allowed Death's Head to smash him.
Motormouth and Killpower later met the Hulk. The Hulk literally fell onto their dinner table after a confrontation with the villain Madman. Killpower and Hulk briefly fought, Harley's foul language was overwhelmed and Madman kidnapped Prince Charles and dropped him off the Big Ben tower.
In the ensuing battle, which involved saving Charles from harm, Harley accidentally knocked down London Bridge. Madman escaped.
Motormouth and Killpower came under the attention of Nigel Orpington-Smythe, leader of the R.C.X. Security footage stills of the two, plus other Marvel UK heroes were shown to Captain Britain as an example of the lawless vigilantism that Smythe sought to control. R.C.X was neutralized before they became a threat to Harley.
Motormouth, like all British super-heroes, was drafted into MI13 during the Skrull invasion of Britain. When Dracula launched an assault on England, Motormouth was injured trying to defend the father of Faiza Hussain.
Powers and Abilities
Harley can create deafening sounds and force blasts by screaming/shouting, similar to the X-Men's Banshee and by humming at a low pitch can use ultrasound to see through solid objects.
She can also jump between alternate universes using the MOPED technology built into her; this technology also allows her to sense threats outside her normal field or range of senses. She also seems to have some ability to sense various forms of energy.