In an effort to hide himself from Unicron (both are psychically linked in their pure forms), Primus separates himself into 5 forms.
The Allspark - a typically cubical to trapezoidal construct that exists on an inter-dimensional plane. The Allspark is the purest fragment of Primus, able to create new life, and "collect" all fragments of Primus no matter where they are in space, time or dimension.
Vector Sigma - the sentient core of a metallic planetoid. It carries out the will of Primus, allowing life and civilization to flourish on the evolving planet. It has direct access to the Allspark.
The Matrix - a device that records the events as experienced by its bearer. The Matrix has the ability to enhance and protect its bearer, and acts as a conduit to the Allspark. It thus has the ability to create life, and influences the bearer and his followers to inadvertently carry out the Will of Primus. There are multiple Matrices across space and dimensions - they often take different forms and names.
Primon - the corporeal mechanoid sent into the world to experience life in the corporeal plane. Primon was the first Matrix bearer, and acted as a distant, cryptic advisor to the Thirteen Children of Primus - Prima in particular. He is unaware of his true nature and identity. Upon Unicron's defeat and exile, Primon ventured into the black hole to find Unicron. He was accompanied by Primacron. Together they found the remains of Unicron. But the Fallen, who had been banished with Unicron, corrupted Primacron, who then betrayed Primon. Primon was sequentially reformatted. The reformatting process split Primon's spark in two - one portion would join the Matrix; the other portion was fashioned into Primacron's Assistant, which eventually evolved into...
The Oracle - an inter-dimensional being of energy that observes the unfoldings of past, present and future in the interest of staving Unicron's progress. It influences Primus's progeny to work against the Unicronian Agenda.