Mayor Richard Wilkins was the main antagonist in the third season of Buffy the Vampire Slayer and was responsible for masterminding a long-running plot that ultimately climaxed in him ascending into a demonic Old One - a gigantic dragon-like demon that proceeded to attack and kill the student body of Sunnydale High during their Graduation but was killed by Buffy via being lured into the school - which had been filled with explosives, thus blowing the monster up and ending his reign of terror.
Mayor Richard Wilkins was once an ordinary human who came to Sunnydale in the past looking for gold. He stumbled across a group of demons and made a pact with them in order to save his own life - stating he would found a town on top of the Hellmouth in order to give demons, vampires and other supernatural evils a place to spread and in exchange the demons granted him immortality that would last for 100 years after the founding of Sunnydale - after which he would be rendered mortal again and lose his chance to "ascend" into a demon himself.
So it was that for the next hundred years Mayor Richard Wilkins ran Sunnydale as Wilkins I, II and III - each time pretending to be the son of the last mayor to avoid detection, he also began to stop having romantic affairs after his wife aged and died while he remained immortal - though he grew to have a strong attachment to the rogue Slayer Faith in the series. This was seen as a more paternal instinct than romantic however and he treated her more as a daughter than a potential spouse.
Unlike most of Buffy's enemies Wilkins was polite, obsessively clean and refused to swear - even when he was trapped in the school and about to die he simply said "oh gosh!" - he was also probably a fairly good mayor in practice, keeping Sunnydale nice and ordered but of course on the inside he was a man who was capable of great evil and ultimately his darkness would be revealed for all the town to see when he became a demon incarnate.
Even before his ascension Wilkins shows his evil side when he tried to smother Buffy while she was in hospital in revenge for her stabbing Faith - luckily for Buffy, Wilkins was scared off by Angel before he could succeed in this attempted murder.
Mayor Wilkins was the first "Big Bad" in Buffy who wasn't a vampire and was popular amongst fans due to his great power and unique personality for a Buffy villain - up until the final battle Wilkins was invulnerable to harm and as such was one of Buffy's more powerful enemies and during his ascension he blocked out the sun, allowing a small army of vampires to rise to his aid - in addition to all this Wilkins was an accomplished sorcerer who had indepth knowledge of the dark arts.
In the end, Mayor Wilkins turned into the demon Olvikan, who ate Principal Snyder and killed Larry with his tail. He was killed when Giles blew up Sunnydale High.
Sometime after his death, his image (human-form) was utilised by the First Evil to taunt Faith later in the series.
- A music video comprising of the Mayor's activities in season 3 - played (fittingly enough) to "The Mayor" by Rasputina.