Unicron is the twin-brother of Primus. Unlike his sibling, he is an antagonist, known as "the bringer of chaos".
History[]
Transformers: Robots in Disguise[]
Years after Unicron's final defeat, when Megatronus was freed and brought to Earth, he used a spark-merging staff to extract the anti-spark remnant from beneath the Earth, intending to use the staff to merge the anti-spark and the Allspark together so as to destroy both Earth and Cybertron. However, when the staff was broken before it could fully draw in the Allspark, the anti-spark remnant then returned to the Earth's core.