In reality the first evil has no true origin the first evil has been around since time began. Even before demons and humans where even thought of the first was there. No demon god or anything cam befo re the First Evil. If you want to read about it there is almost no chance you will because it existed before words where and almost nothing is or ever needs to be written on it. The first has no true form and is actually incorporeal. It cannot hurt anyone nor can they hurt it and it actually doesn't need to hurt some with physical force. It will never end so all it has to do is plan. In reality no one can stop its plans they can only be delayed and even then it will just start all over since it has the time to plan.
The First doesn't h ave a gender nor is it defined by any type of species or race. Any time the first appears it is in the form of a person who had died at any time. During most of the time it fight Buffy if it didn't take on a s hape to torment someone it would walk around looking like Buffy
since she had died at some time. Because the First has been around longer than humans it has had billions upon billions of years to study us and knows us better than we know are selves. The First can talk to someone for just a moment and mess with their mind and drive them almost crazy. The First toyed with Spike for days and turned him from a refor med creature for good to a violent killing machine that killed when ever when told to and would beat himself.
Buffy fought ( as much as you can anyway) at Christmas time in 1998. Angel
had just gotten back to earth from the Hell dimension Buffy sent to him after he got back his soul. The First showed up wanting the pleasure of tormenting Angel with the people he had killed and mostly took on the form of Jenny Calendar
. He al most got Angel to kill Buffy and then almost cause Angel to walk into the sun a nd burn himself to death. At some point after Buffy came back from the dead the first sensed a type of glitch in the Slayers
. The First deiced that because of this moment in time that it would be a good idea to kill Buffy and all the other Slayer potentials and end them once and for all.
Sadly for Buffy this was not a good thing because when the First plans the First plans. The First soon began to increase its activites but its power was so great that many different demons
and beings could sense the First rising up from its slumber. The First would begin to screw with Spike and turning into allot of important people to him such as Drusilla, The Master and even Buffy herself. The First would terrorize Andrew Wells with the shape of Warren Mears
killed by Willow
. It is believed that The First made itself look like Dawn
and Buffy's mother Joyce and tormented her talking about the end of the world that was coming. Using the form of the young girl Cassie Newton it tried to get Willow to stop using magic at all saying Tara told her to because the magic would make her evil, but Willow finally saw through her disguise and The First left.
Soon using its Harbringers the First began to hunt down and kill all potential slayers and there watchers. After placing a bomb in the Watchers council HQ it exploded and killed all of them save for Giles and Wesley who had been fired. Meanwhile the first has been trying to get Andrew to kill his friend Jonathan so that his blood can be used as a sacrifice to open the seal that keeps the Hellmouth shut. If the Hellmouth is opened a number of evils and demons could emerge and turn earth into a new hell. However Andrew did kill Jonathan but his blood was not enough and The First had to move on to another part of its plan. The First tried to get Spike and Buffy to kill each other but soon it realized that Spike would be better suited being used to open the Seal and after its Harbringers captured him it bleed him over the Seal releasing and ancient and dangerous vampire called a Turok-Han. The Turok-Han is called as different as vampires as humans are from Neanderthals. The Turok-Han was sent after Buffy and with its speed strength and vicious killer methods it almost ki lled Buffy.
Meanwhile pot ential slayers where being found and sent to live with Buffy because even though she was beaten she was still the safest place to be. She decided to train the potentials and while they where there she was motivated to fight against the Turok-Han and this time she won and killed the thing in front of them increasing the moral of the group. The First even tried to still get Andrew to work for him and kill the other slayers but that plan failed and like always it moved on. Buffy however was working
harder and harder and even used tears from Andrew to close the Hellmouth. But still the First tormented the potentials and eve had one kill herself.
Soon the First made another powerful play. After finding the location of the Slayer Scythe in the Shadow Valley Vineyard the First used it as its new base and called its most powerful soldier the women hating priest Caleb
had been found by Willow in L.A. helping Angel and she came back to help Buffy. The Slayers tried to attack the Vineyard and it ended badly. Buffy was once again beaten and two potentials where killed and even closer to Buffy Xander's
eye was poked out of his head. This fight caused the Slayers to turn against Buffy and made Faith their leader. After spending a night with Spike Buffy got he courage and fought Caleb and made him look like a foil and found the scythe.
Meanwhile the slayers lead by Faith attacked the Vineyard but all the same they failed after a bomb went off and almost killed them. Once the scythe was in Buffy's hands however she had the strength to fight the First better than ever and wanted to find out about the Scythe. She asked a old and ancient woman about it but when she went to meet with her Caleb killed her and the two fought but Buffy won thanks to Angel showing up. Even after using more power from the First Calbe was cut in half by Buffy Angel gave Buffy a amulet that she in turn gave to Spike and had Willow use to magic in the scythe to turn all the potentials into full blown slayers and with this army they went to the Hellmouth opened it and fought the Turok-Hans soon Spike used the powers of the amulet to kill himself and the Turok-Hans. The blast from the amulet destroyed not only the Hellmouth seal but also the now empty town of Sunnydale. Buffy then went on to other countries making the slayers into a army but even though the First's plan didn't work this time the First will live for on and on and can only see this as a stop gap and is no doubt thinking of something new an even more evil to do.
The first being only energy has no real form nor is it solid. No one can hurt it but it cannot hurt anyone but even so it has no real reason as since it knows some much about people it merely talks to people to drive them crazy and get inside their heads. It makes plans years in ahead. It may spend thousands of years planning since it cannot die and even if its plan don't work at some point it doesn't care because it will just do this all over again.