Uncle Jimmy Thompson (1848 to 1931). The first performer ever on the Grand Ole Opry, in 1925, at age 77.
Why this player is listed
Uncle Jimmy Thompson appears in the Play Bluegrass guide to notable fiddle players, which collects contest champions, bluegrass fiddlers, Canadian fiddlers, judges, and departed legends tied to the tradition.
More fiddle context
For the larger list, start with the big list of fiddle players. For the style itself, read the guide to bluegrass fiddle.