Pope Gregory IX (1147-1241) was probably the world’s worst cat hater or at least he did the most damage to cats. What he did caused the persecution of domestic and stray cats for 500 years.
Pope Gregory IX initiated the feline holocaust in Europe which was to continue through the Middle Ages and beyond.
He issued a public decree or charter (a papal bull) in 1233 in which he denounced the black cat as diabolical. In doing so he gave his official blessing to the widespread persecution of cats. It was already happening in Europe. So he did not really ban cats as encourage others to persecute and be cruel to them.
This set the course for five centuries of torture, burning and hatred of the cat. Records show that in the 16th and 17th centuries, 100,000 witches were legally executed in Germany. In France 75,000 were executed and in Britain the number was 30,000. Where possible cats were destroyed with their witches.
It is estimated that hundreds of thousands of cats were slaughtered at this time and it was encouraged by Pope Gregory IX.