All Souls Day, in the Catholic tradition, was instituted in the monastery of Cluny in 993. According to tradition, there was a pilgrim, returning from the Holy Land, who was compelled by a storm to land on a rocky island, where he found a hermit, who told him that among the cliffs was an opening into the infernal regions through which huge flames ascended, and where the groans of the tormented were distinctly audible.
The pilgrim told Odilo, abbot of Cluny, of this, and the abbot appointed the day following, which was the 2nd, to be set apart for the benefit of those souls in purgatory.
It is not solely a Catholic commemoration though and other faiths adopt it as a day to remember those who have passed on, particularly family and ancestors. As it’s a fine thing to remember those we have known and known of, even for an atheist, it would seem to be a fitting day to do this on.