Despite his execution by fire, Michael Servitus, a Spanish theologian from the sixteenth century, in this day and age would be considered somewhat of a Christian martyr. He was considered a heretic during the sixteenth century because of his non belief in the Trinity, the theology of "God in three persons": the Father, the Son, and the Holy Spirit.
Ironically, John Calvin, a Frenchman, was himself a religious refugee who had relocated to Geneva, Switzerland in order to escape the Inquisition. Once relocated, Calvin became a pivotal figure in both politics and religion; separation of church and state was out of the question. Though Christ, during his earthly existence, maintained that his kingdom wasn't an earthly one, Calvin "legislated" Christianity, inasmuch as he could.
It could be argued that mere semantics were responsible for the hysteria that resulted in Servetus' unfortunate demise. He touted a belief in "Logos", which was Greek for the spoken word of God, in the Person of Jesus Christ. In other words, the manifestation of God was innate within Christ. Christ, in human form, was the literal spoken word of God. Jesus, indeed, according to Servetus, was divine, but he was separate from God.
Additionally, Servetus denounced pre-destination, a major tenet of Calivinism. Servetus believed that God does not send people to hell for no apparent reason; he argued (as did the Catholics) that through a person's own words and deeds only would he face condemnation. Man, he believed, had control over his own spiritual destiny.
For two years, Calvin and Servitus maintained a strained, adversarial relationship, through letters, each trying to convince the other of his corner on the God market.
Calvin's detractors believe that his condemnation of Servitus was primarily a political decision; an effort to appear just as "tough" as the papacy. The Catholic Church condemned Servitus of heresy, and threw him in a French prison, from which he escaped.
What remains puzzling to many is the "united front" between the Catholic church and Calvin, with regards to Servitus. Because he was at odds with Catholicism during the Inquisition, Calvin sought religious asylum, something he was not willing to grant Servitus.
Calvin forwarded letters from Servitus, which served to expedite his execution. However, while Calvin conceded that Servitus should be punished, he requested a more "humane" form of capital punishment: beheading. Customarily, civil disobedience was punishable by beheading; the more serious infraction of heresy earned the perpetrator a date with a burning stake. The official charge against him stated that his unbelief in the Trinity and his denunciation of infant baptism brought about his harsh sentence.
Ironically, Servetus was castigated by both Catholics and Protestants, although the differences between Protestantism and Catholicism were chasm wide, and the source of many a blood battle. Whether Calvin acted through his own political self interest, or simply failed to fully rise above cultural injustice is a moot point. The result was the same, no matter the motive. And, it goes without saying that had Calvin shown Servitus mercy, Servitus destiny would have been quite different.