The bar was marketed under the name "Marathon" in the UK and Ireland until 1990, when Mars decided to align the UK product with the global Snickers name (Mars had marketed and discontinued an unrelated bar named Marathon in the United States during the 1970s which was similar to the UK's Curly Wurly).

Why was the Snickers bar called Marathon?

But to no avail given that people might not have liked them the way mars had planned them to be. The marathon chocolate bar really earned it name because the bar was known to have taken a long time to finish.

When did Marathon change its name?

Mars decided to rebrand Marathon in the UK and align it with the rest of the world. Mars bosses changed the name of Marathon to Snickers in 1990.