Hank Snow was the first person to record this, under the name Hank the Singing Ranger back in 1946 (recorded Dec. 1944).

People credit Bill Monroe's performance (his most famous group, with Flatt & Scruggs) on Feb. 1948 as the "big bang" of bluegrass. Though Monroe himself wasn't actually singing or playing mandolin on that cut, Scruggs plays many of his now-well-known banjo licks.