According to one of his creation who served as his assistant, he possesses a tremendous intelligence and an indefinite lifespan. He devoted most of his time to technological research, developing all sorts of mechanoid lifeforms, from the most primitive simple ones to one of the most complex ones: Unicron, a highly advanced and super-intelligent mechanoid giant humanoid lifeform able to transform itself into a small moon. Primacron planned to use Unicron as a mean of conquest but the giant machine escaped his will and went on a galaxywide rampage, bent on destroying any mechanoid form he met and consumine their raw material.
After the destruction of Unicron by cybertronian mechanoids in 2005, Primacron created Tornedron, a sentient vampiric energy matrix which also escaped his control and was finally defeated by some of his early and more primtive creations in 2006.
Primacron research facilites were destroyed in these events and what became of him afterward remains a mystery.
Source: Transformers "Call of the Primitives"