Jack Dorsey is an American entrepreneur and software developer best known as a co‑founder of Twitter (now branded X) and co‑founder and long‑time leader of the financial‑technology company Block, Inc. (formerly Square). He was born November 19, 1976, in St. Louis, Missouri, and developed an early interest in dispatch systems and programming, which influenced his later projects[1][3].[1] Dorsey helped create Twitter in 2006 while working with Odeo/Obvious and served as the company’s first chief executive officer in 2007–2008 and again from 2015 until his 2021 resignation as CEO; Twitter grew under his leadership into a global realtime social platform[1][3].[1] In 2009–2010 he co‑founded Square with Jim McKelvey, a payments and merchant services company that popularized small‑business card acceptance via mobile devices; Square later rebranded as Block and expanded into broader financial and crypto products[1][3].[1] Throughout his career Dorsey has been associated with several tech initiatives beyond Twitter and Block, including founding the decentralized social‑media project Bluesky and maintaining interests in cryptocurrencies and decentralized protocols[1][3].[1] His work made him a notable figure in Silicon Valley, and he has been a prominent public voice on product design, moderation, payments, and internet decentralization[3][6].[3] Dorsey’s tenure attracted both praise for innovation and criticism over platform governance and leadership style; he stepped down as Twitter CEO in 2021 and continued as Block’s CEO, guiding the company through product expansion and crypto experiments[1][3].[1] As of mid‑2025, major business profiles continue to list him as a significant technology executive and entrepreneur with substantial personal wealth derived from his holdings in the companies he helped build[1][3].[1] Sources: biographical and company profiles summarizing Dorsey’s roles at Twitter/X and Block/Square and his founding activities and public relevance[1][3][6].[1]