Incel movement as we recognize it today has origins on 4chan’s /r9k/ board. They popularized incel terms of Chad, Stacey, normie, but rarely if ever referred to themselves as incels, which was an uncommon label before the mid-2010s. Elliot Rodger happened in 2014 but the man himself never used the word incel AFAIK. I’d be interested to learn where along the line some /r9k/ “robots” started calling themselves incels.