The man whose name is on the guillotine did not build it, did not die by it, and opposed the death penalty. He spent the rest of his life wishing people would forget the connection.
Joseph-Ignace Guillotin was a physician from Saintes and a deputy to the French National Assembly. On October 10, 1789, he proposed that the condemned "shall be decapitated" by "a simple mechanism." His aim was reform. Beheading had been a privilege of nobles, while commoners faced slower and crueler deaths. Guillotin wanted one quick method for everyone, whatever their rank.
The machine itself was designed by someone else. Antoine Louis, a surgeon, worked on the prototype with a German engineer, Tobias Schmidt. For a while the device was called a louisette or louison after Louis. That name did not last. Guillotin had already become linked to the idea after a speech to the Assembly, and his surname won.
French turned the surname into a feminine noun, la guillotine. Etymonline dates the word to 1791, and the verb to 1794. The first execution came on April 25, 1792, when a highwayman named Nicolas Jacques Pelletier was beheaded in Paris.
The idea was not new. Beheading machines had been used before in England and Scotland, including the Halifax Gibbet and the Scottish Maiden, built in 1564. What was new was the attempt to make the method equal for all.
Two myths cling to the name. The first is that Guillotin invented the machine. He proposed it. Louis led the design, and Schmidt built the prototype. The second is that he was executed by it. He died of natural causes in Paris in 1814, aged 75. The confusion may come from a different doctor named Guillotin, from Lyon, who was guillotined.
Guillotin never escaped the association. According to Wikipedia, he deeply regretted that the machine bore his name, and his family later changed their surname. The machine outlived him by a long way. France used it until 1977 and abolished capital punishment in 1981.