Yes, I know the character Sans in the game "Undertale", when I was 12 years old and barely finished primary school (in 2017).
If I remember correctly, at the end of 2015 and at the beginning of 2016, I didn't know that the game would become so famous at that time; whether it came out as a meme, the characters, comic videos made by fans, fanart, parody videos made by SrPelo, tracks made by covers and the soundtrack in this case of sans, its best known track is "Megalovania".
I have no idea why the game became so famous at that time of course.
I got to see the entire gameplay (when I was 12 years old), and the endings too, and I thought it was a company, company, or video game studio, but no.
That was done by a person just like Cave Story.
I think it's kind of, from back in the day, written by an individual who experienced the world of video games at that stage.