Reg,

Don't know if you have seen the documentary You See Me Laughing, but it is based on the bluesmen that those in the Black Keys cite as inspirations. 

https://www.imdb.com/title/tt0363223/?ref_=fn_al_tt_1

It's a really good doc (it might even be for free on Youtube).

One sad thing in it though was how when RL Burnside was finally getting some real financial rewards for his years of poverty, those producing and getting his music out were afraid it was going to mess up the aid money he was getting. 

Also, the soundtrack to Big Bad Love is excellent and has songs from these old bluesmen on it...