Answer:
Julian's ancestors were predominantly pagan until after the age of Constantine.
Constantine was not a true christian, only in name, for he only did so to unite his empire under one
religion. He chose not to be baptized until on his death bed. Having murdered his wife and
illegitimate eldest son; he had much to ask in forgiveness. Julian, having seen the murders
of his family by Christians, put things in perspective.
Having been taught Christian and Pagan literature as a child, Julian had more respect and
love for the latter. He felt that for hundreds of years Rome lived under the protection of the
Gods, why then should his uncle bring about its decline.
Once he was able to be fully think for himself, he chose to be Hellenistic or pagan.
The Christian church gave Julian this negative name in order to discredit him, for
as Emperor, he proved to be a formidable adversary.
His weapon was his words. Through his writings he was able to debunk many of their
beliefs through facts and theory.
In short, an apostate is someone who truly believed in their faith then turned from it.
Julian only followed his heart.