Who was the greatest Dark Jedi ever.

he wasn't a dark jedi. I say VENTRESS!

Dooku went from Jedi Master to Sith.

Maybe Ventress. Or maybe Karko? Both were pretty renowned.

Greatest is an opinion. Xendor certainly became a legend, even 4,000 years later.

As for coolest, Asajj gets my vote.

Coolest is an opinion too. 😛

I meant that I think by greatest he meant Dark Jedi who became legendary for evil deeds or massacres or horrendous acts, etc etc etc. So, Xendor fit. So would Ventress.

xendor didnt have much time to study the dark side, thus holding back his knowledge of the dark side, and his power.

Well, smugglers of the OT times use Xendor's name as a curse.

How many times was Asajj mentioned in NJO?

true. true.