Marius was a wizard who was assigned to guard the entrance of Gringotts Wizarding Bank in 1998 during the Death Eaters' reign over the wizarding world. He and another guard used Probity Probes to search anyone attempting to enter. Both guards were Confuded by Harry Potter on 1 May, 1998 when he and his friends broke into the bank to steal one of Voldemort's Horcruxes from the Lestrange Vault.
The name "Marius" was a Roman family name which was derived either from Mars, the name of the Roman god of War, or else from the Latin root mas, maris meaning "male". Gaius Marius was a famous Roman consul of the 2nd century BC.