Adam is a major character and one of the main antagonists of Routes A and B in NieR: Automata, he is the brother of Eve, despite their android appearance they are classified as machines due to the fact that they were made by machines.
Adam is seen as in the Light Novel that he deeply despises no proper education or care. He thought that if he had to describe this horrible thing that happened to them, he would call it "hatred". He mentions he is a perfect example of that. He wanted to understand why humans took death seriously, as it meant nothing to machines. Aside from his usual self, Adam is seen to be a really good brother to Eve. He thinks that he is obliged to shown more in route B where it shows that he cares for his brother and agrees to play with him. In route D, Adam held Eve with a gentle embrace as he was sleeping in the ark. This also indicates that he has shown his care about Eve more since he is free of malice in the ark. Aside from all of this, it can be shown that Adam is actually a masochist. He enjoys feeling pain as it is part of a human feeling. Even in his eventual death, he doesn't seem upset whatsoever, merely calling it, "so cold."