Priscillian (died 385) was bishop of Ávila and a theologian from Roman Gallaecia (in the Iberian Peninsula), the first person in the history of Christianity to be executed for heresy (though the civil charges were for the practice of magic). He founded an ascetic group that, in spite of persecution, continued to subsist in Hispania and Gaul until the later 6th century. Tractates by Priscillian and close followers, which had seemed certainly lost, were recovered in 1885 and published in 1889.
Read more about Priscillian: Priscillian's Career, Priscillian's Contemporary Following, Continued Priscillianism, Writings and Rediscovery