Doppleganger

If you mean the ones talked about in Quantum Jump, then I can't say if they are real, but the program does work. I guess that is all that is necessary.

Abraham Lincoln claims to have seen his doppleganger.

Well, something freaky happened to me. I was a back-up dancer at a festival, it was for kids and teenagers. My mother came to see me and so did my younger cousin. They announced a girl from another country(a participant, I wasn't her back-up dancer) and for a moment my mother wondered why would I go out on the stage when I wasn't singing because that girl freakishly looked like me. I met her backstage and it was kind of awkward because she was like me but with brown eyes. Later, we introduced ourselves to each other and became friends in the days she was in my city. I did a little research and we aren't related.
But I do not believe in dopplegangers nor that they are bad omens.