Pepe the Frog
Pepe is a cartoon green frog that was sourced from a fairly apolitical humor comic called, "Boy’s Club by Matt Furie". which portrayed teenage monsters.
Some self-described incel forums began sharing emotional states via images of Pepe around the 2016 US presidential election. Although the meme is used less now, it is still being used.
Origin and spread
In one particular, "Boy's club" comic, Pepe is seen with his pants down and urinating, while saying, "feels good man". This image allegedly became popular on 4chan's /b/, or "random" board. While the, "feels good" Pepe meme may not have originated 4chan, it certainly spread to the forums: "something awful", "bodybuilding forums", "Tumblr", and "Instagram"
Katy Perry and Nicki Minaj helped it's spread on Instagram.
In 2015, Donald Trump posted a picture of himself as a cartoon image of Pepe, saying "You can't stump the Trump". This solidified the meme's usage in alt-right circles particularly, but also just any right-leaning political space.
It was not long afterward that 4chan and 4chan-like incel boards began adopting the image of Pepe, mostly as emojis. For example, in an incel chatroom one might have found an image of Pepe frowning, or smiling etc, and people would have posted said emojis to convey various emotions.