Brash, arrogant, and not a solid thinker. He tends to follow his instincts and then worry about the consequences later, which has ended him and his brother in situations that their father has had to get them out of. Adam can be very protective over Cain, and often emotional when it comes down to a sticky situation.
Ontop of his being instinctive, Adam finds himself looking for good times wherever he is, and can be quite the center of the party, when he's not ridiculing it for not being amazing enough for his presence. However, that is rare.
Like his brother, when something has not gone his way, he throws a fit, however differing slighty from his brother in that he holds grudges for immense periods of time. Despite his being instinctive, Adam will hold in his anger and brood before exploding violently.
Adam never calls his father "dad, daddy" or any other such title, he always calls him by his first name or "Mr Acres."
Adam grew up with Cain in a background of extravagance, surrounded with lovely things and everything of his dreams. His father was CEO of Acre Brokerage, a major player in the stock markets. As such, Richard was always away on business or on the phone. Adam took an immediate dislike to this lack of attention, and, being the impulsive child he was, did everything in his power to get Richard's attention.
The antics grew worse and worse, and in Adam's teenage years it became even worse (damn hormones). Adam was always able to get him and Cain into trouble, and Richard always bailed them out of it. It was the only kind of attention Adam could get from him.
Most of all though, Adam liked seeing Cain in trouble. It gave him a feeling of justice to see Cain, the favorite, getting chewed out.
In an ultimate attempt to spite his father, Adam goaded and pried, bribed and weedled, all in an effort to get Cain to dabble with him in the Dark Arts. He had picked up reference to it in various books in his father's library. When he was bored he'd thumb through them, enjoying what he read. With a little further research, he became intrigued with his findings, and learned of rituals to summon forth dark powers.
When the rituals finally worked, Lilith came forth as they had planned. The twins offered their services in exchange for power, and were branded with a pentagram on their hand. Ever since, they've wreaked chaos where they could, still in an effort to get attention.