Frank Mars founded the American company. His son Forrest invented Milky Way, but then eventually quarreled with his dad and was removed from the business. Forrest moved to England, founded his own company, and the Mars bar was his first product: a European version of Milky Way.
Later he inherited the original American business and merged the UK one into it.
When the old man eventually died around 80 year old, he left the business 51% to his wife and 49% to his son, so the mom could keep him in check.
When she passed a few years later, the son got it all, and within a few years, they were completely out of business, and the son sold it for pennies.
All of this is secondhand from the head accountant (that had been there since the 80s) that the son fired immediately upon taking full control of the company. It really was a drama that should have been on television.
(Rival Hershey's ties to Pennsylvania history/culture similarly leaves ideas for National Treasure-style conspiracies in the chocolate world in the early history of control over the national identity.)
Free silly plot ideas for Hollywood or a graphic novelist hoping for Hollywood adaptation opportunities.
Also, the 3 Musketeers candy bars used to come with 3 flavors in the package: chocolate, strawberry, and vanilla. Cost cutting led to eliminating the 2 less popular flavors.
EU had more peanuts, not so sweet and nougat was different, IIRC.