“I yam what I yam,” declared Popeye. And just what that is is likely to become less clear as the copyright expires on the character who generates about £1.5 billion in annual sales.

From January 1, the iconic sailor falls into the public domain in Britain under an EU law that restricts the rights of authors to 70 years after their death. Elzie Segar, the Illinois artist who created Popeye, his love interest Olive Oyl and nemesis Bluto, died in 1938.

The Popeye industry stretches from books, toys and action figures to computer games, a fast-food chain and the inevitable canned spinach.

The copyright expiry means that, from Thursday, anyone can print and sell Popeye posters, T-shirts and even create new comic strips, without the need for authorisation or to make royalty payments.

Popeye became a Depression-era hero soon after he first appeared in the 1929 comic strip, Thimble Theatre. Segar drew Popeye as a “working-class Joe” who suffered torment from Bluto — sometimes known as Brutus — until he “can't stands it no more”. Wolfing down spinach turned Popeye into a pumped-up everyman hero, making the case for good over evil.

Popeye the Sailor made his screen debut in 1933. According to a poll of cinema managers, he was more popular than Mickey Mouse by the end of the Thirties.

During wartime, the Popeye tattoo was etched on thousands of soldiers and sailors, who aligned themselves with his good-hearted belligerence.

The question of whether any enterprising food company can now attach Popeye's famous face to their spinach cans will have to be tested in court.

While the copyright is about to expire inside the EU, the character is protected in the US until 2024. US law protects a work for 95 years after its initial copyright.

The Popeye trademark, a separate entity to Segar's authorial copyright, is owned by King Features, a subsidiary of the Hearst Corporation — the US entertainment giant — which is expected to protect its brand aggressively.

Mark Owen, an intellectual property specialist at the law firm Harbottle & Lewis, said: “The Segar drawings are out of copyright, so anyone could put those on T-shirts, posters and cards and create a thriving business. If you sold a Popeye toy or Popeye spinach can, you could be infringing the trademark.”

Mr Owen added: “Popeye is one of the first of the famous 20th-century cartoon characters to fall out of copyright. Betty Boop and ultimately Mickey Mouse will follow.”

Segar's premature death, aged 43, means that Popeye is an early test case for cartoon characters. The earliest Mickey Mouse cartoons will not fall into the US public domain until at least 2023 after the Disney corporation successfully lobbied Congress for a copyright extension.

Sailor and spinach

— Popeye was added to the Thimble Theatre Olive Oyl strip in January 1929

— Elzie Segar was told to tone down Popeye’s aggression as it was a bad influence on children

— Though it is a myth that he was coopted to promote spinach by the US Government, spinach sales in America rose by a third in the decade after his appearance. A tie-in Popeye Spinach brand is one of the most popular in the US

— Popeye was the first cartoon character commemorated by a statue, in 1937 in Crystal City, Texas, the self-proclaimed Spinach Capital of the World

— Popeye animations, cartoon strips and merchandising generated $150 million a year by the 1970s

— The Popeye’s Chicken & Biscuits chain was named after Popeye Doyle from The French Connection film. It now endorses the cartoon character

— The burger-loving J. Wellington Wimpy character gave his name to the Wimpy restaurant chain

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