Its formulation as a sequence of smile-like character is an art work by an Italian hacker: https://jaromil.dyne.org/journal/forkbomb.html

After all, the same fork bomb could be written in a more understandable way:

bomb() { bomb | bomb & }; bomb 

However, Jaromil wanted to encode a virus in a poetic way, citing him:

In considering a source code as literature, I am depicting viruses as though they were the sort of poems written by Verlaine, Rimbaud et al., against those selling the net as a safe area for straight society. [...] Viruses are a political symptom of a community which continues to be extremely vast and banning them is not the solution to the problems deriving therefrom. The same holds true for anonymity and hacking.

Its formulation as a sequence of smile-like character was popularized by an Italian hacker-artist: https://jaromil.dyne.org/journal/forkbomb.html

After all, the same fork bomb could be written in a more understandable way:

bomb() { bomb | bomb & }  bomb 

However, Jaromil wanted to encode a virus in a poetic way, citing him:

In considering a source code as literature, I am depicting viruses as though they were the sort of poems written by Verlaine, Rimbaud et al., against those selling the net as a safe area for straight society. [...] Viruses are a political symptom of a community which continues to be extremely vast and banning them is not the solution to the problems deriving therefrom. The same holds true for anonymity and hacking.

It must be noted that Jaromil did not invent the bomb, but proposed it as an anonymous art work.