Charlie Patton if you want some of the most absolute bare bones blues stuff. He is often called the father of delta blues.The sound quality of his recordings is atrocious but that in a way is the gritty appeal. I like to imagine myself back in the 30s checking into some cheap hotel in the South, grabbing a bottle of cheap whisky and putting some Charlie Patton records on the gramophone. You won't be able to understand 90% of of what he's saying but it's likely to be about him waking up one morning and finding his woman ran off.
Later on Muddy Waters is good gritty mean sounding blues too.
I have large blues collection but haven't really explored it fully yet. If you're working on the assumption that blues should be rough, raw and gritty, then those two guys are really good.
I know a lot of people think very highly of Robert Johnson, but I just thought he was okay. And that legend of him going to the crossroads and making a deal with the devil is a cool story, but it's a crock. He himself never mentioned that anywhere.