An antagonist is the character in a story who has evil intent. The antagonist(s) is the opposing character to a protagonist, which are the characters that have good intent. Antagonists normally have reasoning for committing acts of evil. Though it is rare, it is possible for an antagonist to be an evil doer committing acts of which a protagonist might through acts which may seem evil, which throw off most readers and characters of a story.
A secondary antagonist is an evil doer who serves to a main antagonist, or a character who is a minor enemy of the protagonist. This does not, however, mean that this character is necessarily evil, just annoying or against the hero or heroine.