Coca-Cola registered “Coke” as a trademark in the United States in 1945.
“Coke” had been used informally as a shortened name for Coca-Cola for decades before the registration. Consumers and advertisers used the nickname because it was brief, memorable, and easy to say.
The trademark registration gave the company formal legal protection for the shortened brand name. Coca-Cola continued using both names, with “Coca-Cola” remaining the formal corporate and product identity while “Coke” became a widely recognized everyday name.
The date is sometimes confused with the earlier history of Coca-Cola’s script logo or with the later development of Diet Coke. Those are separate branding milestones; the United States registration of “Coke” dates to 1945.