Opportunists are villains who will gladly exploit any given situation to suit his or her means, they will commit crimes as and when it suits them do so and will break and form alliances in order to succeed - a great many Neutral Evil types are like this but both Lawful Evil, Chaotic Evil and Amoral versions of this personality exist as well.

• Neutral Evil (the most common type, will take advantage of any given situation in order to benefit oneself, regardless of law, order or good versus evil)
• Chaotic Evil (will take advantage of any given situation in order to spread what they see as chaos and/or evil, in opposition to good)
• Lawful Evil (will take advantage of any given situation in order to gain power for themselves, usually with the aim of oppressing others in the process)
• Amoral (do not actively have an alignment yet are known to be incredibly opportunistic (many real-world criminals would go under this subtype)

Due to its very nature it is extremely rare for Opportunists to be Honorable Villains and anyone "of their word" or obsessed with "playing by certain rules" is also unlikely to qualify as they would value alliances or a fixed plan over Opportunistic thinking.