evil twin

plural evil twins

1. idiomaticA duplicate or counterpart that acts in a contrary, nefarious, or insidious manner.

   As a ploy to discredit the reformist politician, the opposing party had hired a lookalike to act as his evil twin and be seen in a variety of compromising situations.

   2 more examples

   ...we see the flip side, the evil twin, the dark side of addition. Human nature contains both a thing and its opposite in varying degrees of tension, and so for every plus there is a minus.

   2003, Peter Halstead, Sea Sun

   ...[he]..lived his life under [another man's name], becoming his evil twin: Staas bought and sold homes, opened bank accounts, obtained credit, married twice, and was arrested at least three times.

   2004, Bob Sullivan, Your Evil Twin: Behind the Identity Theft Epidemic

   Synonyms: alter ego, changeling, doppelganger

2. computingA rogue wireless access point installed near a legitimate one for purposes of eavesdropping or phishing.