Heinrich Kramer (German: Heinrich Kramer, also known as Henricus Institor; Latin: Henricus Institor) was a German Dominican monk and the author of the well-known treatise on demonology, The Hammer of Witches.

The form of the name “Institoris” placed on the title page of the book is a Latin genitive — the possessive case — and is read as “The Hammer of Witches by Institor.” The Latin word Institor is an exact translation into Latin of the German word Kramer, meaning a small-time merchant.

Heinrich Kramer was born into a poor family. In 1445 he joined the Dominican order in his native city. Until 1474 he studied at a Latin school, learning philosophy and theology.

In 1474, he was arrested for a sermon hostile to Emperor Frederick. He was arrested a second time in 1482 for misappropriating money from the sale of indulgences.

In 1479, after a short stay in Rome, he was appointed inquisitor of the Dominican province of Germania. In the same year he received a doctorate in theology. In 1482 he became the prior of the Dominican monastery in his native city; in the same year he published a pamphlet against the Slovenian Archbishop of Carniola, Andreas Zamometić.

It was Heinrich Kramer who drafted the text of the bull Summis desiderantes affectibus in 1484, which was signed by Pope Innocent VIII. According to the text of the “witches’ bull,” the authorities of the German states were to assist the inquisitors with all their might in the fight against witches.

After the bull was approved, he began an active campaign against witches in the Bishopric of Brixen, including conducting a trial in Innsbruck (the territory of the Holy Roman Empire, with which his career would henceforth be associated). However, representatives of all social classes in the city opposed him. When the affair took a threatening turn, the local bishop, in order to stop the wave of discontent, released the accused women and annulled the inquisitorial sentences. Kramer was told to leave