The Kiasyd are a Lasombra Bloodline with Fae blood in them, which makes them a rather interesting take of vampire in general. However, trying to figure out the background for them is a little complicated, since bloodlines are not in the standard books for the 2nd edition and even the Revised edition doesn’t even mention them in the core book.
When and where was the Kiasyd Bloodline introduced as a sub-splat and in which books it appears subsequently till the 20th Anniversary Edition? Note that novels are out of the scope of this question.
Afaik, it has not yet appeared in 5th edition, but to future-proof, this edition is specifically cut.