He still had Alex's face. It drove him mad. When he cleaned his teeth in the morning, there it was, in the mirror, smiling back at him. If he passed a window at night, the ghost of his enemy would glide by beside him. After a heavy rainfall, Alex Rider would look up at him from the puddles. There were times when he wanted to tear his face off with his nails - and in his early days at the prison he had tried to do exactly that...
~ A description of Julius Grief, the precise clone of Alex Rider.
Oh i'm not like The Flash at all. Some would say i'm the reverse.
~ The Flash's evil counterpart, Reverse Flash
An Evil Twin or Evil Clone, also known as an Imposter or Doppelganger can be a deliberate attempt at creating an evil version of a hero by science or magic, or it can be an alternate version of a hero from a twisted reality or timeline. On some occasions, it can even be a literal twin of both the identical and non-identical varieties. Either way, it also connects to and overlaps with villains who are Incriminators.
They can also be Evil Counterparts, Foils or Copycats, meaning that they share some similarities to the heroes and their backgrounds, or are merely copying certain aspects of the hero or another villain altogether. Some of them take this a step further, to the point they would want to replace the hero altogether (Jill Roberts is a prime example to this).