15Voldemort was not the only wizard to make one
Voldemort used Horcruxes to great success, but he was not the first or only wizard to have used them. The first Horcrux was created by Herpo the Foul, an Ancient Greek wizard and one of the earliest known Dark Wizards. He most likely invented the process for creating a Horcrux,
and he shared Voldemort's snake-like features.
The resemblance is not the only thing he shared with Voldemort, though. Herpo the Foul also bred the first Basilisk, and he was one of the earliest known Parselmouths.
These qualities associate him with Salazar Slytherin, likely making Herpo the Foul one of Salazar's ancestors, which would also make him one of Voldemort's ancestors. It is currently unknown if or how Herpo's Horcrux was destroyed or how he died, and it is possible he is still alive, at least as a spirit.
Although Voldemort did not make the first Horcrux, he may be the only wizard to successfully create more than one Horcrux.