Answer :

Halloween is said to stem from the Celtic festival of Samhain, which was where people would construct bonfires and dress up in costumes to keep evil spirits away. Pope Gregory III (8th century) made November 1 All Saints Day to memorialize saints and martyrs. The night before All Saints Day was then known as All Hollow's Eve, then Halloween. Over the years, it became a more community-involved event with the addition of trick or treating. 
I am not sure who invented it but i know what it is.
Howloween is a holiday that back then on October 31st they thought the dead came to life so they worshipped them. The Christains didn't like what was going on so they named it Howllows Eve  . and Beggers would go to houses and ask to pray for the peoople and in return the people would give back bread that is how it is now you know we get candy