You don't know the whole story until you know his story.
We got our first glimpse of "Klaus" last night in the body of Alaric (read our Vampire Diaries review for a full rundown). Next week, we'll get his long-awaited back story.
April 21, in the episode fittingly titled "Klaus," get ready for:
- Klaus still possessing Alaric (it appears so, at least)
- Katherine-Klaus history in flashbacks circa 1491
- The newly-resurrected Elijah in both eras
- Some seriously pissed-off Damon
I believe the term you're looking for is "OMFG" ...