Is he a giant McNugget that grew moldy and purple, or what?
Grimace is the Tenth Manifestation of Evil from beyond the Realm of Children's Tears and Anguish, hidden in a Void that Imprisoned The 6 Expansions of White. The Grimace can never know death, never know love, or never know contentment.
The Grimace will forever lust for sustenance, the Devourer of the Absurd and Intelligence, peoples fingers are fries to it, peoples heads chicken nuggets. The Grimace can not be stopped, can not be appeased. The Grimace is prone to slumber however and it will regularly enter a sedated state in which its eyes grow wide and a gentle smile would cross its expression.
We should all hope that the Grimace stays in slumber as it has for 118 Billion years. We should avoid rousing the Tenth Manifestation.