October 2As early as the ninth century, a day was set aside to honor angels in general and the archangel Michael in particular. This was September 29, the Feast of St. Michael and All Angels or Michaelmas. But some people, believing that a particular angel is assigned to watch over each human being, wanted to honor their own personal protectors or guardian angels. A feast in their honor observed in 16th-century Spain was extended to the whole church by Pope Paul V in 1608, and in 1672 Pope Clement X set October 2 as the universal day for the festival.
SOURCES:
DaysCustFaith-1957, p. 249
OxYear-1999, p. 400
RelHolCal-2004, p. 101