): Spanish philosopher
Ever heard the expression "we are all somebody else's Jew/Black/Irish/Homosexual/[insert persecuted minority name here]" ?
Well, if somebody did pay a heavy price to learn that, that would have to be Miguel Serveto.
See, Mr. Serveto was not extremely popular with his country's religious authorities, due to rather obstinate controversial religious views. This was extremely bad timing to be a Spanish atheist (or categorized as such), as the Spanish inquisition was all but striving at that time.
When he got arrested and the nasty H word got mentioned a lot, Miguel Serveto took it as a cue to take a leave: he escaped from jail and headed for a more tolerant place to live.
Meanwhile in the good kingdom of France... another man was getting into troubles for his own dissenting religious opinions. That man was Calvin, and after a few years of barely tolerated criticism against the established Catholic religion, he finally had to quickly escape the wrath of the king of France, following one conspiracy too many (l'affaire des Placards, in which he was probably not involved at all).
Actually, things worked out well for Calvin, who was eventually able to take refuge in the city of Geneva and establish an independent state ruled by his principles of austere reformism (see Tragedies of the European Reformation for details): at the time, the first and only place in Europe officially freed from the influence of the Catholic Church.
Well, back to Miguel Serveto: quite logically, headed straight for this heaven of anti-Catholicism where he would at last be able to resume a peaceful life free of religious perscutions... That would sound like a perfect happy ending, right?
Before you get all warm and fuzzy, read on:
As soon as Serveto arrived in Geneva, then all-powerful Calvin looked a bit more closely at his case and, disregarding the fact they were basically fleeing the same religious persecutors, he stopped at the frightening realization that Serveto was a dangerous subversive atheist...
A few days later, on Calvin's order, Miguel Serveto was arrested and burned at the stake (very slowly) for "denying the doctrine of the Trinity and the divinity of Christ".
It bears pointing out that in doing so, Calvin was not in any way trying to oblige the Catholic Church or yielding to external pressure: if anything he would have been only too happy to piss them off.
Thus Miguel Serveto's story should go to prove, if at all necessary, that even the most atrociously persecuted people will gladly turn into persecutors themselves when given the occasion...
I would give a dozen obvious examples involving about every eras, religions and countries, especially in more recent times, but I do not care to get flamed by dozens of hot-blooded morons who would probably fail to see the bitter irony of their "you [insert derogative name of antagonist population here] piece of sh**, how dare you show such intolerance toward my people" messages...
And please if you are an active member of the Spanish Inquisition and feel deeply offended by my unfair treatment of your organization's past activities, feel free to /msg me, so we can talk about it, and abstain from using such pointless cowardice as insult soft-linking. I'll appreciate.
For everybody else, sorry if this just destroyed your last remaining shred of confidence in humankind inner goodness: stop reading History books already and go check out the butterflies and watch little kids running around laughing in the park next door.