The Dark Lady: A Romance of the Far Future — Mike Resnick

An alien art expert is caught in a dangerous hunt for an enigmatic beauty in this science fiction classic by a five-time Hugo Awardâ€"winning author.

For thousands of years the Dark Lady has appeared in portraits across the galaxy, but very little is known about her. She wears only black. She has been seen by many but known by few. And if you do see her, it will be after you've taken your last breath . . .

Alien art historian Leonardo has seen paintings of the Dark Lady before and sees her image again when he comes to work at a human art gallery. There he meets a wealthy old collector who hires him to track down portraits of the mysterious woman. However, Leonardo is not alone in his search. There's an art thief out to make some money, and a man desperate to see the model herself in the flesh.
Legend says that the Dark Lady summons men to great deeds or to their demise. As Leonardo's search begins, his obsession with the woman grows. She will either be the key to his salvation or his destruction . . .