Short answers, pulled from the story.
The English word heresy derives from the Ancient Greek haíresis, which originally meant "choice" or "thing chosen." It also came to refer to the process by which a young person would examine various philosophies to determine how to live, before the term acquired its connotation of dangerous dissent.
Priscillian was the first known Christian heretic to be executed. He was condemned in 386 by Roman secular officials on a charge of sorcery and put to death along with four or five followers. Both Ambrose of Milan and Pope Siricius, despite opposing Priscillian's heresy, excommunicated his accusers and held that capital punishment was inappropriate.
The Edict of Thessalonica, issued by Theodosius I in 380 AD, made Christianity the state church of the Roman Empire and gave heresy its first legal definition. Before this edict, the Church had no state-sponsored mechanism to pursue those it regarded as heretics; afterward, church and state enforcement authority began to overlap.
The last known heretic executed by sentence of the Catholic Church was Cayetano Ripoll, a Spanish schoolmaster put to death in 1826.
Heresy is a belief or theory strongly at variance with established religious doctrine. Apostasy is the explicit renunciation of one's religion, principles, or cause. Blasphemy is an impious utterance or action concerning God or sacred things. The three terms describe distinct offenses in religious law.
Isaac Asimov divided scientific heretics into endoheretics, those from within the scientific community, and exoheretics, those from outside it. He concluded that scientific orthodoxy defends itself well against endoheretics through control of education, grants, and publication, but is nearly powerless against exoheretics, and acknowledged that heresy has repeatedly become orthodoxy over time.