From the French grognard, an old veteran soldier, specifically an old grenadier of the Imperial Guard (Grenadiers à pied de la Garde Impériale); an old complaining soldier
grognard (plural grognards)
1.An old soldier.
2.(games, slang) Someone who enjoys playing older war-games or roleplaying games, or older versions of such games, when newer ones are available. " James is such a grognard, he only plays the original edition of Dungeons and Dragons."