I had this notion for a character, a half Vulcan/half Andorian. Partially because I rather like the idea of someone who looks like a blonde Vulcan with blue skin! But the more I thought on it, the more it seemed the strength of this idea is of someone who embodies a taboo. These two races have been historical enemies and in most ways seem total opposites. Even their homeworlds! One an arid desert, the other a frozen wasteland. One has no moon, the other IS a moon. But more than that, Andorians evidently have four genders. This person, this halfbreed, what gender might they be? Quite possibly something...unique. More, doesn't this mean this person must be the result of genetic engineering?
I suppose the idea of this character appeals to me because she (to pick an arbitrary gender designation--and with a note I want to see more female characters) can work as a magnet for prejudice. Not merely because she's the result of a defacto forbidden union--with Andorians and Vulcans both reacting to her poorly--but as the recipient of false expectations. People would see her behavior solely in terms of her heritage. If she remains calm in a crisis, it isn't because she's developed personal discipline it is because of her Vulcan blood. When she holds her own in a firefight, she's told "Must be the Andorian side!" A subtle but pervasive prejudice, one much more likely to show up among her fellow junior officers since they're less experienced. Yet ironically they're also the ones most likely to (eventually) see her as an individual through constant interaction.
Isn't the concept of a character who is born with parents from two different planets, and is an outcast from both races because of this heritage, a bit cliche?
Can be, without a doubt. All depends upon the execution. God (and the Devil) is in the details. I was trying to describe someone pretty specific, dealing with issues that (for example) the character of Spock didn't really. He thought of himself as Vulcan, and reconciling what he considered his "Human" half with that. My hypothetical character faces a different challenge, not least in that she cannot "pass" for either Andorian or Vulcan.
To give an example of what I mean--both B'Elanna Torres and K'eylahr had the exact same heritage in the exact same universe at pretty much the same time. But they remained two completely different characters, with fundamentally individual stories despite their similarities--such as falling in love with a man of a parent's race and having a child by that person. Yet each was unique, and quite distinct from Spock or Commander Sela (to mention yet another half-breed, who also totally identified with just one side of her heritage).