Robert Anton Wilson credited William S. Burroughs for noticing the 23 phenomena (and also noted James Joyce was fascinated with the date April 23), but it looks like he wasn’t the first to write about it. Fortean blogger Theo Paijmans has dug up some older historical mentions of the 23 Enigma. It looks like the oldest comes from German painter, poet and writer Maximilian Dauthendey. Dauthendey wrote in his book Der Geist Meines Vaters in 1912:

My burdensome fateful number that accompanies me throughout the entire life is the number 23. Twentythree years after the death of my mother my father died, and I can be certain, that always the twentythird of the month delivers some burdening message, a twist of fate, a rare case of luck or an extraordinary case of bad luck…

Paijmans has found some other old examples as well.

Charles Fort Institute: The hidden roots of the 23 Enigma

(via Boing Boing)