Jack Dorsey, Noah Glass, Biz Stone, and Evan Williams launched Twitter in 2006.
The service began as a short-message communication project inside Odeo, a podcasting company co-founded by Williams and Glass. Dorsey proposed the SMS-based status-update concept, and the first tweet was sent by Dorsey on March 21, 2006. The public service was released later that year.
The company was initially called Obvious Corporation after separating the project from Odeo, and Twitter, Inc. was incorporated in 2007. This history explains why some accounts list Odeo or Obvious Corporation when discussing Twitter’s origins.
Twitter was renamed X in 2023 after Elon Musk’s acquisition. The answer to this question remains Twitter because that was the company and service launched by the four founders in 2006.