After whom is December 31 named in the Catholic tradition of Saint Sylvester's Day?

December 31 is named in the Catholic tradition of Saint Sylvester's Day after Pope Sylvester I.

Sylvester I was bishop of Rome, or pope, from 314 until his death in 335. His pontificate took place during the reign of Emperor Constantine I, after Christianity gained legal toleration in the Roman Empire. Later tradition links Sylvester with the dedication of important Roman churches, although some stories about his relationship with Constantine are legendary.

December 31 is his feast day in the Roman Catholic calendar. In several European languages and cultures, the name “Sylvester” therefore became associated with New Year's Eve, including German “Silvester” and related terms in parts of Central Europe.

The date is not a universal name for the celebration. English normally uses “New Year's Eve,” while Saint Sylvester's Day is especially common in countries with particular Christian historical and linguistic influences. The holiday name refers to the saint's feast, not to the date of his death being known with modern precision.