Nobody's really got a good definition (that I've seen) over what early Country music is. It's definitely before Elvis forced the then-emerging dominance of Nashville into the first Country-Pop called 'Countrypolitan'. But is it before Hank Williams Sr. or after? Does it include Lefty Frizzell and Johnny Bond and the "Honkytonkers"? Webb Pierce?

In any case I recommend all of Hank Williams, and, looked at in a different way than usual, Bill Monroe.

And seconding Stewie, the great "Brother Acts" of the 1930s and 1940s. Bailes Brothers, Bailey Brothers, Monroe Brothers, the above mentioned Delmore Brothers, and the Blue Sky Boys (Bolick Brothers). And the Louvin Brothers. And Chrlie Poole and the North Carolina Ramblers. Some of the Old Time musicians mightn't like my mentioning these as country, but that's what these artists thought they were.