Herbert Moon is notable for his constant and unabashed anti-Semitic rhetoric, often greeting his customers by asserting that nothing in his shop is Jewish made, how he considers everything he says to be perfectly correct, and his over-the-top sense of pride and confidence, made evident by the way he says his name almost every time he talks to the player. This is reflective of prevailing anti-Semitic attitudes consistent among Americans during that time period. Herbert Moon can be heard accusing "the Jews" of various nefarious plots and influences, like controlling various companies and agencies, even being responsible for the death of President Abraham Lincoln. In addition, Herbert Moon claims Abraham Reyes is "as much of a revolutionary as Napoleon" and just likes "riding horses and wearing a fancy uniform" (however, from what the player sees of Reyes, this is an accurate description).
As the owner of the General Store, Herbert Moon will sometimes appeal to the player to help intervene after being robbed by an outlaw. Additionally, the player has the opportunity to rob and/or kill Herbert Moon themselves.
Herbert Moon can be found working behind the counter in his shop, or playing poker in the back room at the Saloon in Armadillo. Around night-time, when he is not playing poker, he can often be found drinking in front of his shop.
In Undead Nightmare, during the survivor mission "Dinner for Two", John walks into the General Store and asks Moon if he has seen Jonah or Eli. Moon asks if they are Jews (since their names are generally common Jewish names) before going on a rant about the infection, blaming every ethnic minority (Jews, Catholics, Natives, the British and homosexuals, among others) for causing it. John, realizing that Moon is of no help, comments on how remarkably hate-filled he is then walks outside as Moon follows. Moon asks John if he wants to join him in his fight. John refuses and Herbert goes on his own, but is quickly assaulted by three Undead. While being eaten, he shouts, "You can't eat me, I'm Herbert Mooooon!" while John looks on, with a smirk on his face. Afterwards, Herbert Moon comes back as a fresh Undead, and the player may kill him, hogtie him, or flee.
After listing all of the types of people he hates, he proudly admits to never meeting the vast majority of them.
Herbert Moon will often, but not exclusively, refer to himself in third-person.
Herbert Moon has been known to inexplicably shout "I'm Herbert Moon!" when in combat, robbed, or threatened.
If the player enters his store they are usually greeted by a statement like "This establishment welcomes you!" he may even say this if the player enters the store when he is away, Such as when he goes on a cigarette break.
Herbert Moon seems to believe that John Marston is "a hired killer for the Jews." This is possibly a reference to Edgar Ross and Archer Fordham.
There are actually two Herbert Moons present in the game. One plays poker, and the other is the shopkeeper. He can be playing poker and watching over his shop at the same time. This usually only happens during the day, however.
At the end of the day, he can be seen going into the saloon, indicating that he plays poker in the meantime.
If the player duels Herbert Moon and wins, Herbert Moon will still be present in the store. Sometimes, immediately after being killed, another Herbert Moon will instantaneously spawn, and inspect his own corpse.
Herbert Moon is usually unarmed, except when catching the player cheating during a game of poker. When the duel is issued, he will then be seen wearing a gun-belt and holster, carrying a Cattleman Revolver.
If the player instigates a fistfight with Herbert Moon and then draws a weapon, Herbert Moon will pull out either a Repeater Carbine or a Winchester Repeater and start shooting. As long as the player doesn't shoot him first, the local law officers will come after him and a gunfight will begin. When shot by NPCs, Herbert Moon can take a ridiculous amount of bullets; this can lead to humorous results, seeing the owner of a general store single handedly take on the Armadillo law enforcement. After winning the fight (a very likely occurrence), and if his legs are not incapacitated, Herbert Moon will return to his shop and begin serving the player again. This only works with the shopkeeper version of Herbert Moon, not his poker playing version. The poker playing Herbert Moon has normal NPC health. This glitch is not unique to Herbert Moon, however he is the most infamous subject; other shopkeepers, including Jeb Murphy, Alejandro Duarte and E.H. Kretzschmar have this characteristic.
The player should watch out with tying up Herbert Moon. If Marston doesn't keep an eye on him by turning away, Herbert Moon will untie himself and proceed to shoot Marston.
If Herbert Moon is killed in a duel, the player will never be informed that a shopkeeper has been killed, where as if the player kills him outside of a duel, a notification regarding his death will appear and his shop will be unavailable for five days, as with all other shopkeepers.
Herbert Moon acts as a regular NPC in the Armadillo Poker room at the back of the saloon; if he is killed, the player won't be informed that a shopkeeper has been killed and that the shop will be unavailable for five days, however.
If the player kidnaps one Herbert Moon, then leaves Armadillo, upon returning it is possible to gather three Herbert Moons.
In Undead Nightmare, his appearance is more detailed and has a different, scruffier hairstyle.
Herbert Moon does not understand sarcasm well, as in Undead Nightmare when he mentions his hatred for Jews, Natives, Blacks, the British, women, Fabians, socialists, Asians, Catholics, and homosexuals, John jokingly asks if he had ever met a British Catholic homosexual, with Moon taking a few seconds to comprehend.