Short answers, pulled from the story.
Square Enix was officially created on the 1st of April 2003 following the merger of Enix and Square. The company traces its origins to the 22nd of September 1975 when Yasuhiro Fukushima opened a small office in Tokyo that eventually became Enix.
Square and Enix merged to decrease development costs and compete with foreign developers after Square suffered a financial failure with Final Fantasy: The Spirits Within in 2001. The merger took effect on the 1st of April 2003 to combine Square's in-house development with Enix's publishing capabilities.
Square Enix completed a takeover deal for the UK-based publisher Eidos in April 2009. This acquisition brought Western franchises such as Tomb Raider, Hitman, and Deus Ex into the Square Enix portfolio.
Yosuke Matsuda replaced Yoichi Wada as president of Square Enix following the major restructuring announced on the 26th of March 2013. The restructuring was initiated to address sluggish sales of major Western games and an expected loss of 10 billion yen.
On the 1st of May 2022, Square Enix announced the sale of several assets including Crystal Dynamics, Eidos-Montréal, and Square Enix Montreal to the Swedish games holding company Embracer Group. The sale also included iconic franchises such as Tomb Raider, Deus Ex, and Thief.