Darth Grievous

Spoiler warning: Plot spoilers, such as the fact that

DARTH GREVIOUS ONLY EXISTS IN GENERAL GREVIOUS'S MIND

may follow. Read on at your own discretion.

Darth Grievous
Biographical information
Homeworld	General Grievous's mind
Born	Some time between now and then
Died	He died??? I didn't know that!
Physical description
Species	(More) Evil alter ego
Gender	Male programming
Height	The tallest tree on Kashyyyk
Hair color	All I know is, he's bald!!! And he was wearing a mask, duh
Eye color	It was yellowish, much like his ego's
Cybernetics	Hmm... maybe he is, maybe he's not
Chronological and political information
Era(s)	That was around the time when people having copied DNA fought with overcharged drink dispensers...
Affiliation	Sith
Known masters	Darth Sidious
Known apprentices	None that I heard of

[Source]

"You will not stop me this time, Jedis. Hah hah, I said it. Jedis. I'll say it again. Jedis..."

―Grievous

Darth Grievous was the imaginary alter ego of General Grievous. Unlike the general, he totally kicked Jedi ass. He never lost a fight. He was known to destroy your planet for no reason whatsoever. He was a killer of over 16,000 Jedi and was fond of referring to them as "Jedis", much to their annoyance.

Training in the ways of the Dark Side

General Grievous was trained by Count Dooku, which was the reason he lost. Darth Grievous, on the other hand, did not train under the Count. Moreover, Dookie did not even know about his existence. When Count Dooku was training the General, Darth Sidious was concurrently secretly training Darth Grievous in the ultimate Sith classroom. The only Jedi who could top Darth Grievous was the frog dude, though they never met.*Dammit...*

Grudge

Darth Grievous had a grudge against General Grievous because the latter beat him in a fight. He is currently pursuing the general in hopes to destroy him and discover the true nature of the Sarths.