Hephaestus/Hēphaistos/Vulcan- a god of blacksmiths, technology, fire, sculpting, metals and volcanoes.
The craftsman for the gods he was the son of Zeus and Hera or just Hera alone according to some sources. When Zeus birthed Athena from his head without a parent (her mother was Metis, swallowed by Zeus) Hera was jealous and so conceived Hephaestus without help but he was lame and she cast him down from Olympus in disgust, or he was ugly and she cast him down possibly resulting in his lameness. He was then rescued and raised by Thetis and/or Eurynome.
Some sources argue with this as it is sometimes said that it was he who cracked open Zeus' skull to free Athena, thus making him older than Athena. In this case he was cast down from Olympus by Zeus for trying to save Hera when Zeus bound her by her wrists and ankles for trying to overthrow him with Poseidon and Athena. Hephaestus was then rescued by the Sintians on Lemnos.
In revenge for casting him out, Hephaestus carved a golden throne for Hera and gifted it to her. When she sat on it however she became permanently stuck and Hephaestus abandoned her to this fate. Ares came after him to try and force him back by Hephaestus chased him away with torches. Dionysus then came and got him drunk and brought him back in this state and/or promised him Aphrodite as a bride. Hephaestus freed Hera and Hera welcomed Dionysus as an Olympian in thanks.
He was married to Aphrodite but she was unfaithful to him, particularly with Ares. When Helios informed Hephaestus of their affair he set a trap for them, an invisible net about their bed. When the lovers were trapped he brought the other gods to shame them. Only the males came and Poseidon offered to pay Ares' adulter's fee if Ares did not. Homer, Pseudo-Apollodorus and Nonnus all suggested that Hephaestus divorced Aphrodite for this affair.
He then punished the lovers further by gifting their daughter Harmonia with a cursed necklace on her wedding day. The curse did his work damning her and her descedants.
As a craftsman he crafted many things- weapons, armour, jewellery, palaces, automans- and in one case, a person, specifically the first woman Pandora. He made her from clay and all the gods gifted her with something- Athena robed her, Hermes named her and gave her a voice and trickery, Aphrodite gave her grace and longing, the Charites gave her necklaces, the Horae a crown and Zeus gave her a jar/urn/box/pithos with all the evils in it. She married Prometheus' brother Epimetheus despite Prometheus' warnings and opened the urn unleashing evil onto the world.
Feeling that Prometheus was not yet punishing enough for stealing fire for humans and helping them earn the better part of meat, Zeus had Hephaestus chain Prometheus to a rock where he suffered an eagle feeding on his regenerating liver daily. Hephaestus may have had extra motive as Prometheus was said to have taken the fire from Hephaestus' own forge.
He drove out Adranus/Adranos a fire god from Mt. Etna/Aetna and put his forge there. This mountain was believed to have been named after one of his lovers, the nymph Aetna.
Like many of the other gods he fought in the war against the Gigantes, killing the giant Mimas with molten lava (sometimes Ares is said to have killed him).
His side during the Trojan War is unclear, Homer describes him as having a deep loyalty to his mother Hera who was on the side of the Greeks but he saved the son of Trojan priest Dares, Idaios from Diomedes and yet forged armour for the Greek Achilles at his mother Thetis' request. During the war he also fought the river god Skamandros/Xanthos when he tried to drown Achilles.
He could be kind as well as vengeful as demonstrated by his saving of Idaios. He also aided Orion after he had been blinded by Oenopion for raping his daughter when drunk. Hephaestus gave him his servant Cedalion to be his guide and Orion carried him on his shoulders until he guided to him Helios who cured his blindness, he then returned Cedalion to Hephaestus after that.
When Pelops was killed and served up as food by his father Tantalus and Demeter ate a shoulder, after the gods restored him it was Hephaestus who gave him a new shoulder, of ivory.
For the gods he built palaces and thrones of marble, gold and bronze. For himself he made golden maidens and automans to help him with his work. For Helios he made a golden boat. For Apollo and Artemis he made bows and arrows. For Athena and/or Zeus the Aegis. For Hermes his winged sandals and helmet. For Aphrodite her girdle.
He built things for mortals as well as the immortals, fashioning gold and silver dogs to guard King Alcinous' palace. He also built a palace for King Aeetes as thanks to his father Helios, who had rescued Hephaestus during the war with the Gigantes. He also made for him fountains with gold, silver, bronze and iron basins that gushed out water, milk, wine and oil, and bulls with bronze hooves that breathed fire. For King Minos he built the bronze giant Talos who ran round the island of Crete three times a day guarding it. He made a wine bowl for Menelaus and a sceptre for his brother Agamemnon.
For many heroes he made weapons. For Perseus his sword, for Achilles' armour, for Heracles' armour, a quiver and bronze rattles to chase off the Stymphalian Birds, for Eos' son Memnon armour, for Diomedes a cuirass, and for Aphrodite's son Aeneas, armour.
He was helped in his forge by the Cyclopes, his automans and his sons/helpers the Cabeiri/Cabiri/Kabiri/Kabeiroi.
Though Aphrodite is his most infamous partner Hephaestus, despite being lame and ugly, did have other lovers, even another wife. Aglaea/Aglaia was the youngest Charite/Grace (daughters of Zeus and Eurynome) and was given as either an alternative wife for Hephaestus or his second wife after he divorced Aphrodite. She was a goddess of beauty, splendor, glory, magnificence and adornment and in an interesting twist was a handmaiden of Aphrodite along with her sisters, she was also sometimes a messenger for Aphrodite. With him she had four children- Eucleia/Eukleia (Good Repute and Glory), Plutarch strangely said she was a child of Heracles and Myrto (whose brother was Patroclus) who died a virgin and became a goddess; Eupheme (Acclaim, Praise, Good Omen), her opposite was Momus the god of satire and mockery, and sometimes she was said to have nursed the Muses and had a son Krotos/Crotus, a hunter who kept company with the Muses and invented applause, with Pan; Euthenia (Prosperity), her opposite was Penia/Penae, the personification of poverty and need and Philophrosyne (Welcome, Friendliness, Kindness). These sisters became members of the younger Charites and attendants of Aphrodite.
Hephaestus attempted to rape Athena when she came to him for weapons and he was overcome by beauty. She fled from him but his seamen spilt on her leg, she wiped it off and cast it down to earth, causing Gaia to be impregnated by it. From this union Erichthonius/Erichthonios a future king of Athens was born. He was put in a box by Athena and given to the Athenian king Cecrops' daughters- Herse, Pandrosus and Aglaurus to mind but Herse and Aglaurus opened the box and went mad from the sight killing themselves. They saw the infant either with two snakes or in a form half human and half serpent.
Along with Apollo, Hermes and Ares he tried to woo Persephone with a gift. He offered her a colourful necklace but either she or her mother Demeter turned the suitors away.
Aitna/Aetna was a nymph, a daughter of Ouranos and Gaia or Gaia and the Hecatonchire Briareus. She was arbitrator between Demeter and Hephaestus over Sicily and with Zeus or Hephaestus became mother to the Palici/Palaci/Palikoi, gods associated with geysers, and Thalia/Thaleia a nymph associated with plant life and shoots who was abducted by Zeus in the form of an eagle and is sometimes said to be the mother of the Palici rather than the sister, sometimes Adranus/Adranos is given as the father of the Palici with Thalia.
With Cabeiro/Kabeiro, a sea nymph, he had the Cabeiri/Cabiri/Kabeiroi/Kabiri and the Kabeirides, they were a mystery group of deities who varied in number and were chthonic (associated with the underworld). They varied in depiction, starting out as deities who protected sailors then becoming an old man and his son, Axiocersus and Cadmilus and a female duo, Axierus and Axiocersa. Strabo said their mother was a daughter of Proteus and Rhea but that they had no father. They became craftsmen who helped Hephaestus.
With Anticleia/Antikleia, a mortal woman, he had the bandit Periphetes/ Corynetes a bandit who was lame like his father and had one eye. He killed travellers with a bronze club and was killed by a boulder by Theseus.
Ardalos/Ardalus was a son who invented the flute and built a temple to the Muses.
Cerycon/Kerykon a bandit and king of Eleusis was given as another son though sometimes his father was Poseidon or Branchus. He challenged people to a wrestling match and killed the loser. Theseus killed him.
Olenos/Olenus was another son and a king who fathered Helice/Helike and Aex, nymphs who nursed Zeus when he was an infant. (Obviously this would mean he was around before Zeus and therefore could not be a son of Hephaestus who came after Zeus was grown).
Palaimonios/Palaemonius was a son and one of the Argonauts.
Philottus/Philottos was another son, possibly the same Philottus who was married to Niobe and killed himself when she brought down the wrath of Apollo and Artemis after insulting their mother Leto, leading to the death of all their sons and daughters.
Pylius/Pylios was another son, who cured Philoctetes/Philocthetes of his wound when a snake bit him when he trespassed on the shrine of the nymph Chryse. (In other sources it was Machaon or Podalirius, both sons of Asclepius, who healed Philoctetes.)
Hyginus gives him another son, Spinther, but says nothing about him.
He was depicted as a cripple, usually ugly and at work over his forge or anvil. Sometimes his feet were back to front and he had a stick to aid him. The donkey, crane and fennel plant were sacred to him. The fennel plant was used as a torch in ancient times as it burnt slowly. His symbols were the tongs, anvil and hammer.
His Roman counterpart was Vulcan/Vulcanus, initially a god of fire he was associated with it as both a useful and harmful element. People prayed to him to prevent harmful fires. He was linked to male fertility as well. He was the patron of trades linked to ovens. He was thought to originate from Velchanos, a Cretan god of fire who accompanied the Great Goddess (Cybele), and who was associated with vegetation and springtime.
He was also father to Cacus/Kakos a fire breathing giant who ate humans and nailed their heads to his door who was killed by Hercules after he stole some of the cattle that Hercules had stolen from Geryon for his Tenth Labour. He was given a sister Caca, who some say betrayed him to Hercules. Another son was Caeculus/Kaikalos, a king whose mother was impregnated by a stray spark from her hearth. She exposed her son and he was found by a fire by a group of girls who brought him to his real uncles, the Depidii. He grew up with shepherds before founding the city Praeneste. He could conjure and extinguish fire and was unharmed by it though his eyes were damaged by smoke, making them smaller than normal. He fought against Aphrodite's son Aeneas with Turnus. A third son was another Roman king, Servius Tullius. His mother was Ocrisia, a noblewoman who became slave to Tanaquil, wife of king Tarquinius but was still treated with respect. She either became wife to a friend of Tarquinius or a Vestal Virgin. She was impregnated by a phallus that appeared within the flames she was tending.