“Pee Wee” Gaskins
This guy (real name Donald Henry Gaskins), terrorized America during the 50’s and 60’s.
Known for his small stature, he was a rapist who started his spree at the age of 12. In and out of reformatories, mental hospitals and prison, he escaped for the last time and joined a circus. He raped and murdered across the US for a few years.
In the 70’s, he bought himself a hearse and started attacking hitchhikers and tourists, claiming that he needed the back space for his victims.
In 1976, after he had over a hundred victims under his belt, he was imprisoned for a life sentence, until he was caught murdering another inmate and given the electric chair.
You forgot Harold Shipman, probably the world's most prolific serial killer and a doctor.