Hephaestus is the lie that all Greek Gods were handsome and beautiful. He was the ugly runt of Olympus, a smelly misanthrope only tolerated because he could make a mean suit of armour or household furniture for his fellow divinities. The Romans called him Vulcan and Hollywood Spock. He is usually portrayed as a bearded man with a bad limp - the result of falling out of Olympus after a drinks too many or chucked out by Zeus for preventing his mother Hera receiving a marital beating (depending on which myth you follow).
Birth and Family
Hephaestus was the brother of Ares the God of War. He also had a sister called Hebe who was essentially the maid servant of everyone else on Olympus until she married Hercules. Hephaestus's parents (Zeus and Hera) were appalled at the sight of their ugly son and banished him from Olympus. Instead Hephaestus lived amongst the wood nymphs and the tooth fairies, learning to become a handyman God. He could build shelves, hang pictures and forge new armour on request. He loved his mother but that wasn't returned by Hera. The Greek Gods had a collective cruel sense of humour (as witnessed by their constant interference in human matters back on Earth) and made jokes about Hephaestus's ugliness.
Unwisely, Hephaestus who was fed up witnessing his father's constant infidelities, stood up to him in an Olympian 'domestic' which saw the bigger god pick him and throw him out of the family abode. Hephaestus eventually landed on Earth and retreated into a cave to sulk. His bones didn't properly heal and left him with a permanent gammy leg.
Hephaestus would have stayed there but it didn't take long for Olympus to turn into a student residence with broken windows and furniture turning that place into a nightmare. Even the taps stopped working. Hephaestus held out, naming his price that he be provided with a goddess wife. His first choice was Athena but she refused, claiming she wanted to remain a spinster. Second choice Aphrodite likewise objected but Zeus threatened that if she didn't take Hephaestus, he would send down to hell become Hades's wife. Aphrodite caved in, extracting a promise from her new husband that he would build a new kitchen at their new marital pad.
Marriage and Infidelity
Hephaestus tried to make Aphrodite like him. He made a magic girdle for her, a sparkly belt that would inspire instant love/lust/desire from a man who saw it. Since Aphrodite was attractive enough, this seems to have been an unnecessary present but the goddess in turn hired out her present to the other female gods to get their male counterparts horny. Oddly, Hephaestus failed to make one for himself so that he would be desirable to other women (the girdle was for heterosexuals only) which would have prevented what happened next. Aphrodite had no interest in her husband's main line of business - forging weapons - and preferred to stay at home on her couch. This encouraged Ares to come round to entertain her whilst his brother was out.
Ares's getting his jolies irked Apollo. He was upset that Aphrodite had preferred the God of War to the Brain Box (self description) and told Hephaestus he was being cheated on. To Apollo's surprise, Hephaestus didn't react like a Zeus and go divinely mental. Instead he worked out a plan to shame and humiliate the cheating couple.
Working late nights at the forge, Hephaestus constructed a metal fishing net. However it was so finely done that you couldn't see unless right up close. This was then hung over the couch where Aphrodite liked to receive Ares (minus all their clothes). A rope was attached on a pulley hidden near the wall. The trap was now set.
Pretending to go to work, Hephaestus instead sneaked himself into a side room and waited. Ares turned up at the usual hour to be greeted by Aphrodite. He didn't have to wait long for the sounds of love making and poked his head around the door. Seeing that his wife and brother were heavily engaged in the beast with two backs, Hephaestus went round the back of the bed. The net dropped on the couple, its weight pinning both Aphrodite and Ares in the act of copulation. Hephaestus exclaimed in joy and anger and limped off to the other gods to see what he had done. Zeus, Poseidon, Hermes and Apollo quickly followed,overtaking Hephaestus to view the erotic tableaux. The Greek Goddesses stayed away, in embarrassment rather than sisterly solidarity.
The male gods laughed at first but then changed their looks to appear more sympathetic to Aphrodite. Zeus thought the whole business in bad taste (!) and blamed Hephaestus for neglecting his wife for hanging out at the smithy with his one eyed workforce known as the cyclops. He then imposed a fine on Ares for cheating and then told Aphrodite to spend some time on Earth to 'cleanse herself'.
Athena and Thetis
Hephaestus saw little of his wife or the children - especially when he discovered after a paternity test that they were his brother's kids. Instead he consoled himself with work and hobbling after a few available minor goddesses in return for making them trinkets. Only Athena remained a regular visitor, dropping off her armour for upgrades and polishing. One time Hephaestus insisted she strip off because the padded armour he made required no under clothes. Athena complied, only have the randy old blacksmith attempt to 'ravish' her by the fire pit whilst the staff took a liquid lunch. Hephaestus shot his load like a nervous teenager on a first date. Athena surprisingly took this assault within in her stride but threatened to 'geld the God' if he tried that move again.
Another Goddess to have her integrity mucked around with was the Thetis, the mother of Achilles. She came to the forge with an express order for a suit of armour for her boy to made and fashioned in one night. Hephaestus agreed if Thetis provided some 'extras'. Achilles got his armour the next morning.
The Romans adopted Hephaestus's back story and called him Vulcan. He did the same as his Greek counterpart and was equally ugly and grouchy. He was also a bit meaner and nastier, with a 'vulcanic' temper that would see a lot of ironmongery flung around the forge. Later on Star Trek creator Gene Roddenberry chose 'Vulcan' as the name and civilisation of the Commander Spock. Spock was normally coldly logically and not given to temper tantrums unless his 'human' side got grabbed by lustful thoughts. Nor did he appear to have a limp.