Sorachi Hideaki (空知 英秋) is the original author of the Gintama manga, which the anime was adapted from. There exists a cameo of this manga author in the form of a gorilla drawn by the author himself. The gorilla usually wears a yellow T-shirt with the red kanji (俺, ore, lit. 'I' or 'Me') on it. His cameo has made appearances in both the Gintama manga and anime.
There is also yet another cameo of this (gorilla) cameo in the anime series by the name of Amachi Hideaki. This other anime cameo is a more realistic gorilla which only grunts, contrary to the manga author's more anthropomorphic version, which speaks human language, and whose voice-over in the anime series is done by the author himself.
As a follow-up on this joke, the anime quickly began to deteriorate without its original manga author, but somehow managed to pull through after Sorachi had been rebuilt as a cyborg, as commented by Shimura Shinpachi in the next episode.