The exact origins of this being are unknown; what is known is that it previously lived on an inhabited planet where it used its abilities to turn the inhabitants against each other. Even on the occasions when it was discovered, it was able to use its abilities to escape, and the infighting from its actions eventually led to the planet's destruction. The One became marooned on a fragment of the planet, a large asteroid, where it spent an unspecified period of time languishing in boredom without other beings to manipulate, imitate, and/or deceive. Eventually The Four Golden Weapons ended up on the comet as a result of the events of Wrong Place, Wrong Time, and after the Nindroids escaped with them the One was left to torment their stranded Ninja pursuers.
The One Who is Many attempted to prevent the Ninja from repairing the Arcturus spacecraft and making their escape, impersonating Kai, Jay, Cole, and Nya in its efforts. It eventually abducted Jay and forced the others to follow it to a series of ruins, where it made known it's role in the cataclysm that had destroyed its previous home. Taking the forms of Lloyd, Wu (both normal and cyborg), and Cyrus Borg, it refused to allow the Ninja to leave. However, Zane was eventually able to defeat it by tricking it into attempting to copy his Nindroid form, which left it temporarily stunned and allowed the ninja to escape.
The One Who is Many possesses the ability to assume a variety of shapes and forms, and can also imitate voices given it's ability to deceive the Ninja. It appears to have some telepathic abilities, as it was able to take the forms of individuals known to the Ninja that it had not encountered, and could produce various items of clothing in its disguise. The One also appears to have some knowledge of engineering, as it was able to create a hovercraft for itself using parts from Project: Arcturus, as well as tactics. It could assume alien and human forms, including a featureless white Minifigure, and could transform itself into smoke as well. However, for some reason it was apparently unable to take the form of an inorganic Nindroid, and the attempt temporarily weakened it and allowed the Ninja to flee.