Sorry, Conor McGregor ... Georges St-Pierre believes Royce Gracie -- not you -- is the greatest MMA fighter of all time.
And, he's praising the "UFC 1" champion for paving the way for everyone else!
"Royce Gracie is the one that really changed the sport," GSP tells TMZ Sports ... "[He] changed the entire belief system of what a real fight is."
Gracie is a LEGEND -- who famously won 3 FIGHTS IN A ROW IN THE SAME NIGHT at UFC 1 back in 1993.