When human, Spike was known as William. He was an Upperclass citizen of London, who never really fit in, he was constantly teased by everyone he knew, and was rejected by the woman he loved. He became a vampire, partly by choice, as he was sick of his horrible life. Drusilla sired him, and Spike joined Angel, Darla and Drusilla's gang. Spike was not very controled, most likily killing everyone he knew. This lead to some problems, as angry mobs came after Spike and the rest of the vampires he was tagging along with. Angel was furious, and told him of the Slayer. Spike decided to seek her out, this is very uncharacteristic of a vampire.
He was able to find and kill the slayer in 1900, and from then on he got more and more powerfull, and a lot more respect.
In 1977 he killed another slayer in New York city.
Years later, in 1997 He came with Dru to Sunnydale in an attempt to find a way to heal Dru. He attempted to take over
The Master's place as ruler, but he couldn't kill the current Slayer. He was therefore denied the position and instead
killed The Anointed One and took the position forcefully. Spike was injured by the Slayer when he kidnapped
Angel to use in a ritual to restore Dru to full health. He was paralysed and was unable to walk,
so Dru had to take care of him for a while. At about this time, Angel had lost his soul again, and had started to woo
Dru away from Spike. Spike grew very jealous,
and when Angel planned on raising Acathla, he contacted The Slayer and joined with her in a plan
to stop Angel. Spike pretty much just beat Angel with a crowbar then left
town with Dru.
He didn't return until a few months later, after Dru had left him for
betraying Angel. He kidnapped Willow so she'd make a Love Spell for him. However, after getting
into a large fight with old Vampire minions, Spike realised he didn't need Dru any more. All he
needed was a spot of violence to feel good again, and so he left town.
Spike didn't return to Sunnydale for about
another year. This time he returned to look for The Gem of Amara. He also started a romantic relationship with
Harmony. After getting the Gem, he took on the Slayer, but when she removed the gem from his
finger, he was forced to retreat. Buffy decided to send the Gem to Angel. Spike followed the Gem
to LA and eventually captured Angel. He hired Marcus to torture the
ring's location out of Angel. When Spike finally got the ring though, Marcus stole it, and
Spike was left with nothing.
About a month later, Spike went back to Sunnydale to get even with The Slayer. Before he
got the chance, he was captured by the Initiative, a goverment run organisation that handeled super natural creatures like
vampires. He managed to escape, but not before they had ensured he could no longer harm any humans.
Since he couldn't drink blood from living people any longer, he was forced to go to The Slayer for help.
Spike soon figured out that the chip did not limit him from killing demons, only humans. This made him form an uneasy
alliance with The Slayer, she would pay him, and give him blood, while he could do things to risky for a humans.
Overtime, he began to change, he developed a deep desire for a romantic realationship with The Slayer, Spike has always
desired Slayers, but now that he couldn't kill, it became a romantic interest instead. He even gave up a chance with Dru
to stay with her. Eventually, The Slayer realised the Spike might be a souless monster, but he also was trying to reform.
Spike has killed two slayers in his time, once drinking the blood, which would probably have added a little to his
strength. Spike is also quite sunlight resistant, in the sense that the flame doesn't consume and spread, but just burns
in one area. He also was able to recover from a terrible back injury in only a few months. Overall, for his age, he's in
good shape, better then average.