I thought of a list of things that would have never happened if Katherine wasn't here, and I came up with a good bunch.

1. Without Katherine, Stefan and Damon would have stayed human and died a long time ago.
Katherine made Stefan die and become awesome, and with that he turned the Damon we all amor into himself. So she practically gave us the hot, badass Damon we all adore so much.
2. If it wasn't for Katherine, Elena wouldn't have been even born.
If Katherine didn't have a Baby and that baby didn't have a baby and that baby didn't have a baby etc. there would have been no Elena would there?
3....

She has all of the powers and weaknesses of a vampire.

Transfigured in 1492 unintentionally por Rose (unintentionally on Rose's part), she is as a result much mais powerful than the Salvatore Brothers who she turned after she had been a vampire for 372 years but much less so than Pearl was who was turned sometime in the 1430s about sixty years before Katherine. A demonstration of how much mais powerful than the Salvatore Brothers was when she easily defeated them in two fights with each brother. Another demonstration of her immense physical strength is when she snapped the iron shackles that...