Alternately, Alex, who originally had good or neutral intentions, has been working for the Big Bad for so long that he lost all of his original morals and descended into a state of apathy toward his work, allowing him to do things which he once would never have considered without a twinge of guilt or remorse.
Zig Zagged: Alex tells The Hero that the reason that he became a psychopath is to avenge the death of Betty, who he loved. However, The Hero later learns that Bob lied about his Freudian Excuse. He recaptures Alex and is told a completely different story altogether.
The reason why Alex is evil or amoral is never revealed.
Alex had a normal background. He became evil for simple reasons, like wanting money.
Enforced: "We really ought to explain why Alex does what he does. Otherwise he'll just look like just another Card-Carrying Villain."
Lampshaded: "You don't know why I'm this way, do you? This looks like a good time for me to tell you my tragic and unhappy backstory."
Invoked: "All right, Alex, tell us what made you the slime you are!"