Priscillian

Priscillian was the first person to be excommunicated and executed (that we know of) because of his "heretical" beliefs. I use the quotation marks because this was a time (4th century) when official church doctrine was still in a state of flux and because some of his writings were perfectly acceptable and even embraced for awhile.

He was born in Gallaecia (now northern Portugal) c.340, to a noble family. He preached and practiced a strict form of asceticism starting about 370. This involved celibacy—women were treated equally as men and praised for being virgins—and fasting on Sundays and Christmas Day.

He taught that not only Holy Scripture should be read and studied, but also some of the texts that were considered apocryphal—not because they were inspired revelation like the canonical works, but because they could be helpful in discerning truth from error. He wrote his own commentary on the Pauline epistles, organizing them according to their theological points and writing an introduction to them. They include the call to asceticism and abstinence from meat and wine. Some Spanish manuscripts of the Epistles have Priscillian's writing still attached. The ideas are the same, but the text differs from any of Priscillian's original works; they were apparently re-written by a Bishop Peregrinus. (His originals were thought lost, but a copy was discovered in 1885 at the University of Würzburg.)

His ideas caused him to clash with others, however. His major opponents were Bishop Hyginus of Corduba (Cordova) and Bishop Hydatius of Augusta Emerita (Mérida, Spain). They accused his ideas of being gnostic. Hydatius spoke out so much that he drew more attention to Priscillian's teachings than condemnation of them. 

Hydatius convened a synod in 380 at Caesaraugusta (Zaragoza/Saragossa), with 10 bishops from Spain and two from Aquitaine. Priscillian was not invited. The synod declared, without mentioning Priscillian or his ideas, that one could not assume the title "doctor" of the church, that women were not to be called "virgin" un til they were 40 years old, that clerics were not to embrace the monkish life just because they were motivated to live more perfectly. 

Living an ascetic life and promoting celibacy made Priscillian look good, however, and he was made Bishop of Ávila, Spain in that same year. That's when things really got contentious, but we'll save that for tomorrow.