While seeing Episode III, I wondered, "What exactly is General Grievous?" He has to be some sort of life form because we can see his eyes, heart, etc. through his droid-like exterior. Was Grievous always his name, what was his past, why is he like that? Let's analyze what we know:

Grievous is/was an alien or possibly a humanoid: I would assume that he was an alien because of the yellow eyes, but what kind, we don't know. Some have suggested that he may have been a Dug because of his dextrous feet. Some have wished that Grievous was the remains of Darth Maul. That's a little farfetched for me, but we don't know for sure.

Grievous is no longer an alien or humanoid: Grievous now resides inside a metal body which protects the remains of his flesh. We know that Grievous must have a brain to connect to his eyes, and a heart, because we see it in the film. He must also have some sort of blood vessels and possibly lungs to account for his difficulty breathing. He may also still have vocal cords or some throat organs allowing him to cough. He must feed these organic parts with some type of nourishment. How? I don't know!

Since Grievous has organic parts he should be able to use the Force: I didn't understand this in the movie. Since he was training under Dooku, he should have been able to learn some Force powers. In the Lego Star Wars game, Grievous can't use the Force which really bugged me while I was playing it. Midi-chlorians reside in all living cells according to Qui-Gon so why didn't Grievous use the Force except maybe to aid in his lightsaber skills.

Is there any EU that tells Grievous's history? I'm curious. I welcome any thoughts and new ideas.

"Army or not, you must realize, you are doomed!" -Grievous