>>1506811Anon made a thread about it on /co/. They had a series of threads. Soon posting of pony images made their way to /b/ and communities developed on both boards. Those people made other websites, such as Equestria Daily. People that weren't channers picked up on it and visited those sites, and it grew into a fantom that way. Moot made /mlp/ to take the pony spam off other boards. Within a year or two nearly all of the original channers got tired of the dumb fandom shit and went to /mlp/, having never left since while the fandom morphs into an abhorrence outside 4chan.
