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No, Peter was not a Gnostic.
The Gnostic Paul was created in 1975.
The Gnostic Preludes was created on 2012-03-13.
He was an ardent follower of gnostic beliefs and precepts.
That is the correct spelling of "gnostic" (capitalized Gnostic referring to the belief).
The similar word is the adjective or noun agnostic(neither a theist nor atheist).