what is he using?

im a big fan of Gustave Dore illustration.
because of the awesome texture and everything
and the only question is.....what kind of stuff
did he put into his art?

ink or charcoal?

Ink obviously, such high detail cant be charcoal.

It's hard to say, if you have the right Charcoal you can handle doing really small details. Judging by the contrasts and fading i'd go with charcoal on this one. The darks in the pictures look kind of grey-ish and with Ink you typically get that dark black finish with very little fading.

On the first picture it definitely looks like it's just regular crosshatching.

On the others I have no idea. Watery china ink perhaps?

It looks like that the top one is pen and ink, but the others seems more of a mixed media of charcoal for the smudges and pen to add the details...