Written by Kristina
Adam was a creation of Maggie Walsh's - a modern day Frankenstein. He was created in the depths of the Initiative from human, robot and demon body parts. His human origins are unknown - what is known was that he was created as a super soldier for the secret government agency. Unfortunately, nobody told Adam this. He rose from the operating table, and killed his creator - his mother - and left the Initiative lab to learn more about himself and the world around him. He left behind a trail of dissected humans and demons in an attempt to learn how he worked, and more about the world around him.
Buffy and Xander infiltrated the Initiative lab in order to find out what was happening to its soldiers (at this point, Riley was going a little…nutty), and met Adam for the first time. He confronted Riley (who followed Buffy in) and shared that Maggie was both of their mothers. Apparently, there was more to Riley's role in the Initiative then just a favored soldier.
Adam disappeared into the background, but not for long. He had a plan - and for this plan, he began to recruit both demons and vampires to his side. In an uncharacteristic move for the different demon races, they foght side by side against the Slayer, and allowed themselves to be captured by Initiative soldiers. As the cells in the Initiative began to fill to overflowing, a chink in Adam's armor was discovered, by none other than (superstar-ified) Jonathan - Adam's power source was Uranium-235, located inside his body. Get rid of the power source, get rid of Adam.
Adam, however, was the only person in Sunnydale unaffected by Jonathan's spell. As a kinematically redundant, biomechanical demonoid, he was hyperaware of himself and his surroundings. He also had a plan, but in order for it to work, he needed the Slayer separated from her friends. For this, he enlisted the help of Spike, and agreed to remove Spike's chip after he successfully completed his task. (Unfortunately for Spike, this meant ripping off his head.) He gave Spike top secret files about the Initiative to pass on to the Slayer and her friends to draw the Slayer into a final showdown.
Of course, Spike alienated the Slayer from her friends before the information could be decoded, but all was not lost - the Slayer and her friends came together (and resolved their differences for the time being), and headed off to the Initiative to face down Adam. Putting his plan into motion, Adam released the caged demons, and they attacked the scientists and soldiers in the complex causing utter chaos. All along, Adam's plan was to create maximum carnage to provide him with the body parts to create more evil super soldiers, like himself. And Riley was a part of this plan as well - Maggie Walsh placed a control chip in Riley's chest, tied to his thoracic nerve, that could be activated when the time was right. And Adam activated it, for unclear purposes.
Adam knew the Slayer would not be strong enough to face him alone, which is why he had Spike alienate the Slayer from her friends. What he hadn't counted on was them performing an enjoining spell to create a "Super Buffy." "Super Buffy" held her own very well against Adam, and his demon/human/robot mind could not comprehend how she was able to defeat him. He fired bullets at her, tried to attack her, but nothing worked. He could only watch in disbelief as "Super Buffy" reached into him, and ripped out his power centre. He fell to the ground, useless.
Or at least, useless as a corporeal being. When the First Evil returned to Sunnydale almost three years later, it assumed Adam's form while haunting Spike. One thing is certain in the Buffyverse - death is (rarely) final.