Hephaestus (also Hephaistos) is the Greek god of fire and the forge. He is called Vulcan or Mulciber ("softener") in Roman mythology and Sethlans in Etruscan mythology. He is the Greek God of the forge, blacksmiths, craftsmen, artisans, sculptors, metals and metallurgy and fire. He is either the son of Zeus and Hera or of Hera alone in jealousy for Zeus' solo birth of Athena. He was worshipped in all the manufacturing and industrial centers of Greece, especially Athens. He was also associated with Mount Etna in Sicily.
In Athens there was a Temple of Hephaestus and Athena called the Hephaesteum or Theseum, located at the foot of the Acropolis. Hephaestus, along with Athena Ergane (patron of craftsman and artisans), were honored at a festival called Chalceia on the thirtieth day of Pyanopsion.
The Zeus and Hera strain of stories holds that Hephaestus split Zeus' head open with a hammer thus releasing Athena. Either way, in Greek thought, the fates of the goddess of war (Athena) and the god of the forge that makes the weapons of war (or at least their births) were linked. Hephaestus also crafted many of Athena's battlements, along with those of the rest of the gods and the mortals who received their favor.
He also crafted many of the other magnficent equipage of the gods, e.g. Hermes' winged helmet and sandals, the Aegis breastplate, Aphrodite's famed girdle, Achilles' armor, Heracles' bronze clappers, Helios' chariot, Eros' bow and arrows and Hades' helmet of invisibility with the help of the Cyclopes and Cedalion, his assistants in the forge. He also built automatons of metal to work for him in his forge, which was believed to lay beneath any of a number of volcanoes in Greece.
Prometheus stole the fire that he gave to man from Hephaestus' forge. Hephaestus also created the gift that the gods gave man, the woman Pandora and her famous box.
Hephaestus was also quite ugly; he was crippled and misshapen at birth. Either Hera or Zeus, mortified to have brought forth such grotesque offspring, promptly threw him from Olympus. He fell many days and nights and landed either in the Ocean where he was brought up by the Oceanid Thetis (mother of Achilles) and Eurynome. Alternatively, Hera threw him from Olympus after he sided with Zeus in an argument. He fell for nine days and nights before landing on the island of Lemnos where he grew to be a master craftsman and was allowed back into Olympus when his ability and usefulness became known to the gods. His forge was located on Lemnos.
Hephaestus gained revenge against Hera for rejecting him by making her a magical throne which, when she sat on it, didn't allow her to leave it. The other gods begged Hephaestus to return to Olympus to let her go but he repeatedly refused. Dionysus got him drunk and took him back to Olympus on the back of a mule. Hephaestus released Hera after being given Aphrodite as his wife.
Alternatively, Zeus took pity on him and arranged his marriage to Aphrodite, either Hephaestus' sister (if she was the child of Zeus and Dione or great aunt (if she was the very much delayed result of the seed of the castrated Uranus falling into the sea). Aphrodite was none too pleased with that turn of events and promptly began an affair with Hephaestus' brother Ares. When Hephaestus found out about it (most likely from his sister Eris, the goddess of discord) he surprised them during one of their trysts and covered them with an invisible and unbreakable net and left them exposed for all of Olympus to see.
One legend claims Hephaestus wanted to marry Athena but she refused him. Alternatively, Athena disappeared from the marriage bed but Hephaestus did not notice and ejaculated on the ground, producing Erichtheus.
He was later married to Aglaea, the youngest of the Graces and fathered several children with mortals and immortals alike. One of those children was the robber Periphetes.
Hephaestus was somehow connected with the mysterious cult of the Cabari.
In art, Hephaestus was shown crippled, ugly and lame and bent over his anvil. He walked with the aid of a stick.
With Thalia, Hephaestus was sometimes considered the father of the Palici.
In Roman mythology, Vulcan was the father of Caeculus.