The TAG Group was owned by the Ojjeh family. In the late '70s/early '80s they were a sponsor of Williams in Formula One.
In 1983 Ron persuaded Mansour Ojjeh (son of the founder) to change from being a sponsor (of Williams) to being a 50% owner of McLaren. This resulted, among other things, in the TAG-badged Porsche engine that for a time was very successfully run in McLaren F1 cars.
In '85 TAG Group bought the Heuer watch company, which had been in business for many decades and which itself was already involved in racing sponsorship. New watch company was called TAG Heuer.
In the late '90s, TAG Group sold TAG Heuer to LVMH, which owns a lot of pretentious, overpriced fashion brands, such as Dior, Louis Vuitton, Hublot, and Loewe, and wines and spirits companies such as Dom Perignon, Krug, Hennessy and Moet & Chandon.
Although TAG Group sold off the watch business years ago, it retained its ownership stake in McLaren Group. Although its percentage ownership has fluctuated over the years as first Mercedes became a shareholder, then the Bahrainis became shareholders, then Mercedes sold, the TAG Group and Mansour Ojjeh have always had a shareholding in McLaren Group equal to Ron's.
The status of TAG/Ojjeh's shareholding has been the subject of speculation in the last year or two. Mansour Ojjeh's health was problematical (he had a double lung transplant), and reportedly his family have been pushing for the stake in McLaren Group to be sold. I have no idea where that stands now.