Vulcan (Latin: Vulcanus, in archaically retained spelling also Volcanus, both pronounced [wʊɫˈkaːnʊs]) is the god of fire including the fire of volcanoes, deserts, metalworking and the forge in ancient Roman religion and myth. He is often depicted with a blacksmith's hammer. The Vulcanalia was the annual festival held August 23 in his honor. His Greek counterpart is Hephaestus, the god of fire and smithery. In Etruscan religion, he is identified with Sethlans.

Vulcan belongs to the most ancient stage of Roman religion: Varro, the ancient Roman scholar and writer, citing the Annales Maximi, records that king Titus Tatius dedicated altars to a series of deities including Vulcan.

The origin of the name is unclear. Roman tradition maintained that it was related to Latin words connected to lightning (fulgur, fulgere, fulmen), which in turn was thought of as related to flames. This interpretation is supported by Walter William Skeat in his etymological dictionary as meaning lustre.

It has been supposed that his name was not Latin but related to that of the Cretan god Velchanos, a god of nature and the nether world. Wolfgang Meid has disputed this identification as fantastic. Meid and Vasily Abaev have proposed on their side a matching theonym in the Ossetic legendary smith of the Nart saga Kurd-Alä-Wärgon ("the Alan smith Wärgon"), and postulated an original PIE smith god named *wl̩kānos. But since the name in its normal form is stable and has a clear meaning—kurd ("smith") + Alaeg (the name of one of the Nartic families)+ on ("of the family")—this hypothesis has been considered unacceptable by Dumezil.

Christian-Joseph Guyonvarc'h has proposed the identification with the Irish name Olcan (Ogamic Ulccagni, in the genitive).^{[citation needed]} Gérard Capdeville finds a continuity between Cretan Minoan god Velchanos and Etruscan Velchans. The Minoan god's identity would be that of a young deity, master of fire and companion of the Great Goddess.

According to Martin L. West, Volcanus may represent a god of the fire named *Volca and attached to the suffix -no-, the typical appendage indicating the god's domain in Indo-European languages. *Volca could therefore be a cognate of the Sanskrit words ulkā (उल्का) ("flame, meteor, firebrand") and/or várcas- ("brilliance, glare").

Vulcan's oldest shrine in Rome, called the Vulcanal, was situated at the foot of the Capitoline in the Forum Romanum, and was reputed to date to the archaic period of the kings of Rome, and to have been established on the site by Titus Tatius, the Sabine co-king, with a traditional date in the 8th century BC. It was the view of the Etruscan haruspices that a temple of Vulcan should be located outside the city, and the Vulcanal may originally have been on or outside the city limits before they expanded to include the Capitoline Hill. The Volcanalia sacrifice was offered here to Vulcan, on August 23. Vulcan also had a temple on the Campus Martius, which was in existence by 214 BC.

The Romans identified Vulcan with the Greek smith-god Hephaestus. Vulcan became associated like his Greek counterpart with the constructive use of fire in metalworking. A fragment of a Greek pot showing Hephaestus found at the Volcanal has been dated to the 6th century BC, suggesting that the two gods were already associated at this date. However, Vulcan had a stronger association than Hephaestus with fire's destructive capacity, and a major concern of his worshippers was to encourage the god to avert harmful fires.