From Halopedia, the Halo wiki
The TheRealYapYap is a satirical twitter account purporting to be that of Yapyap the Destroyer, run by an unidentified 343 Industries employee or group of employees. The account was created on March 28, 2018 to coincide with the first Yappening, an occasional event in 343 Industries' games, in which Yapyap takes control of the game and adds a variety of wacky changes and gamemodes. The Twitter features Yapyap's thoughts about several Halo-related subjects, often asserting his superiority over them or threatening to destroy them. He appears to have a rivalry with Yabda, a fellow Unggoy. Yapyap often interacts with and responds to other notable Halo-related Twitter accounts, including the official Halo Twitter account.
During his tenure on Twitter, Yapyap has mentioned a number of characters in the Halo universe. Some of these have been existing characters while others were entirely new ones. Those in the latter category are not considered canonical.