For More Indepth Info see the TFWiki article.
Onyx Prime is one of the original 13 Transformers, of his brethren he was known as the "Lord of Beasts". He was responsible for modifying the genes of the Zoidians, and creating the Zoids, The Zoid Eve, and mechafauna galaxy wide. He and his brother, Nexus Prime, would be responsible for the creation of Voltron in the Pegasus Galaxy.
Onyx was supposedly a caring and gentle soul at heart, compassionate about his fellow prime and being, but able and willing to defend them with the ferocity of a dragon.