While clowns as a role are very old - see for example the related role of the Court Jester, which dates back to 1800 BC - the term Coulrophobia was only coined in the 1990s. However, it is a clinically known condition that affects many people worldwide.
The origin of Coulrophobia can usually be found in a traumatic childhood experience.
Coulrophobia is occasionally mentioned in works of fiction. Among the more notable ones would be the Simpsons-inspired meme "Can't sleep, clown will eat me" (a catchphrase which in turn was named after an Alice Cooper song), and the Batman villain Joker is an insane clown who intentionally instills people with this fear.