TUI AG (trading as TUI Group) is a German multinational leisure, travel and tourism company; it is the largest such company in the world. TUI is an acronym for Touristik Union International ("Tourism Union International"). TUI AG was known as Preussag AG until 1997 when the company changed its activities from mining to tourism. It is headquartered in Hanover, Germany. It fully or partially owns several travel agencies, hotel chains, cruise lines and retail shops as well as five European airlines.
https://en.wikipedia.org/wiki/TUI_Group