The second species to join the Citadel, the salarians
are warm-blooded amphibians native to the planet Sur'Kesh. Salarians
possess a hyperactive metabolism; they think fast, talk fast, and move
fast. To salarians, other species seem sluggish and dull-witted,
especially the elcor. Unfortunately, their metabolic speed leaves them with a relatively short lifespan; salarians over the age of 40 are a rarity
Salarians are known for their observational capability and
non-linear thinking. This manifests as an aptitude for research and
espionage. They are constantly experimenting and inventing, and it is
generally accepted that they always know more than they are letting on.
The krogan are a species of large reptilian bipeds native to the planet Tuchanka,
a world known for its harsh environments, scarce resources, and
overabundance of vicious predators. The krogan managed to not only
survive on their unforgiving homeworld, but actually thrived in the
extreme conditions. Unfortunately, as krogan society became more
technologically advanced so did their weaponry.
Due to the brutality of their surroundings, natural selection has played
a significant role in the evolution of the krogan. Unlike most species
on the Citadel, krogan eyes are wide-set - on Earth
this is distinctive of prey animals, but in this case it gives the
krogan 240-degree vision, giving them greater visual acuity and
awareness of approaching predators.
Their large shoulder humps store fluids and nutrients, enabling them to
survive extended periods without food or water. A bigger shoulder hump
is seen as a sign of high status, showing how successful an individual
krogan is at hunting. Their thick hides are virtually impervious to
cuts, scrapes or contusions, and they are highly resistant to
including toxins, radiation, and extreme heat and cold. Consequently
their diets can include food and drink which would prove very dangerous
to other species.
"Wilkins arrived in California in the 1899 where he found Sunnydale after the last slayer died there, which lay over the Hellmouth for demons to feed on on the promise of an Ascension. He became mayor of Sunnydale to keep an eye on everything, making sure nothing would interfere with his demon transformation plans, but remained out of the spotlight so as not to attract attention of any would-be interlopers.
After Mayor Wilkins achieved Ascension into a gigantic, snake-like pure-demon during Sunnydale High's graduation ceremony in 1999. Buffy lured him into the empty library, now filled with bags of dynamite. Rupert Giles then pressed the trigger that obliterated the Mayor and the school building.
The essence of the Mayor survived and possessed the bodies of dead animals and demons as well as vampires to get revenge on Buffy. In the process, he was responsible for the creation of Adam, when he possessed the corpse of a powerful demon (his earlier vampire body having been captured by the Initiative) and badly injured the then-human Adam. He also put Buffy's watcher Giles in the hospital, killed several of Buffy's former school mates and nearly killed Willow, In his final battle with Buffy in Faith's apartment, Buffy finally learned of his ghostly nature after decapitating his current body to no effect. Willow, with the assistance of Xander and Buffy, sent Wilkins to the next realm. There was no evidence that they ever discovered it was the Mayor who had been attacking Buffy, although Faith later told Angel in prison that she recalled the Mayor's ghost visiting her using the body of a dead bird while she was in her coma."(source)