Wikipedia
"Whipping Tom" was the nickname given to two sexual attackers in London and the nearby village of Hackney. Both would attack women walking alone and beat them on the buttocks.
While there is some evidence that an earlier attacker in around 1672 was also nicknamed "Whipping Tom" and carried out similar attacks on women, the earliest recorded attacker of this nature was active in central London in 1681. He would approach unaccompanied women in alleys and courtyards and spank them on the buttocks, before fleeing. The inability of the authorities to apprehend the offender caused complaints about the ineffectiveness of London's constabulary, and prompted vigilante patrols in the affected areas. A local haberdasher and his accomplice were captured and tried for the attacks.
A second attacker nicknamed "Whipping Tom" was active in late 1712 in Hackney, then a rural village outside London. This attacker would approach lone women in the countryside, and beat them on the buttocks with a birch rod. Around 70 attacks were carried out before a local man named Thomas Wallis was captured and confessed to the attacks.