The guard is an exceedingly rare human monster in NetHack that will only appear occasionally if a player is in one of the dungeon's many vaults. They are under the employment of Croesus, and are the source of the footsteps you may hear on some levels, indicating there is a vault on that floor. Guards are mercenaries that are very similar to Yendorian Army soldiers, and can even be bribed.
As mercenaries, guards follow similar generation mechanisms to soldiers and watchmen for armor and weapons; see that article for more details.
Like previously indicated, guards are not randomly generated, and only appear if the player waits around while within a vault, creating an opening in the vault wall or the outside solid rock for them to stand in. Vault guard generation increments the born counter, but does not respect extinction; while there is no limit on how many guards a vault may generate, only one will appear at a time.
Interacting with guards
If you are visibly present in a vault when the guard appears, they will ask you for your name. If you reply with Croesus, Kroisos or Creosote, they will believe you and disappear; this incurs a small alignment penalty for lying if you are lawful, unless it is also your actual name. Attempting this after killing the actual Croesus will cause them to turn hostile.
If you are in a polymorphed state from eating a mimic corpse when a guard appears, they will not notice you and leave, puzzled; doing so while hallucinating produces a different message, but otherwise has the same effect. Polymorphing into a form that can hide under items produces the same message. If you are unable to speak from paralysis, unconsciousness, being in the middle of engraving, or else being in a form that prevents speaking, they will also leave. The guard will not notice you if you are invisible when they enter, and will leave when you move away from them.
Otherwise, upon giving them a name, they will ask you to drop all of your gold and follow them out of the vault; this includes any gold you have in open inventory and in containers within your inventory, so stashing cannot fool them. Once they see you have no gold, they will open a passage from the vault to a nearby corridor in the dungeon and wait for you to follow them out; both the guard and passage will vanish once you safely reach the corridor. Items left inside the passage will be embedded in the solid rock; any monsters caught in the disappearing passage will be moved to a random location on the current level. If you attack the guard, attempt to escape by some other means, or take too long to comply, they will become hostile. If a guard dies in the passageway they create, it will close immediately; their corpse and possessions will be left embedded in stone, along with you if you were also in the passage.
As fighters, guards are able to move at the same speed as an unhasted hero, with an AC that is usually 0 or less, similar to a sergeant; however, they can deal more damage than even Yendorian captains, who have the same monster difficulty. Their sole weapon attack that can hit for up to 40 base damage (incidentally the same as Croesus's weapon attack); the rub of this is that, as described above, guards are very easy to avoid fighting, and are usually not worth bothering anyway.
Their presence can be useful for players who happen upon a vault completely by accident and have no other means of escape; after dropping their gold and following the guard out, they can grab a means of digging (e.g. a mattock) and go back to the vault to retrieve the gold. Once players can reliably make their way in and out of vaults, e.g. via digging or controlled teleports, the guard is little more than a minor obstacle, and a quick lie will get them out of your hair. Some players name their character Croesus (or one of the acceptable variants) to avoid the alignment penalty for lying, although this is only a concern for lawful characters; even for other lawful characters the penalty is small, and in most cases can be easily remedied.
As long as you drop all your gold, they will escort you out; if you pick up the gold again, they will demand you drop it and turn hostile if you do not comply quickly. However, you can freely teleport it away or throw it outside of the vault instead without angering them. While guards can be bribed, since they are already peaceful, this will likely turn them hostile, and is often a waste of gold even when successful; that said, it can be used in some corner cases, e.g. to pacify a hostile guard and avoid risking penalties for murder.
Lawful and neutral vault-hunters who have dealt with Croesus and cleared Fort Ludios will want to avoid using Croesus's name or its variants when answering guards, since this will immediately turn the guard hostile; killing a guard counts as murder, even if the guard attacks you first. However, most characters at this point will have a means to quickly enter and leave vaults as they please, and can avoid dealing with guards in the first place, much less turning them hostile.
Chaotic characters are not penalized for murder, and can theoretically farm guards for items, but will still suffer an alignment penalty for killing a monster designated "always peaceful". Most of the items a guard will have are generally not worthwhile, since there is usually no shortage of barracks and soldiers in a given game; any character that can defeat a guard is usually more than capable of handling those. As such, guard farming is usually only of interest to extinctionist players, as well as chaotic players who have somehow exhausted any other reliable source of items and can somehow soak up the alignment penalties.
Should a player dealing with a guard somehow get stuck in a disappearing passageway, they can pray to escape; being stuck in a wall is considered a major trouble, and a successful prayer will teleport them out. If teleportation somehow fails, the player will be granted temporary phasing for a few turns, which should be enough for them to make it back onto a safe square.
- You hear the footsteps of a guard on patrol.
- A vault is present on the level.
- You hear someone counting money.
- The vault still has its gold inside.
- You hear someone searching.
- The vault's gold is missing.
- Suddenly, one of the vault's guards appear!
- A guard entered the vault while you were present.
- "Hello stranger, who are you?"
- The guard can see you; this will give you a prompt to enter your name.
- "Most likely all of your gold was stolen from this vault."
- The guard is aware of the gold in your inventory and wants you to drop it all.
- "Please follow me."
- The guard is leading you out of the vault, opening a passageway through the solid rock.
- "Drop all your gold, scoundrel!"
- You attempted to pick up the dropped gold again while in their view.
- "So be it, rogue!"
- The guard becomes hostile because you did not drop the gold in time or else refused to.
- "Oh, yes, of course. Sorry to have disturbed you."
- You told the guard you are Croesus, causing them to leave.
- "Back from the dead, are you? I'll remedy that!"
- As above, but you have already killed Croesus; the guard will become hostile.
- "I'll be back when you're ready to speak to me!"
- You were in an impaired state that prevents you speaking when the guard entered, and they left.
- The guard turns around and leaves, puzzled.
- You were not visible when the guard entered, causing them to leave immediately. This is the result of eating a mimic corpse or polymorphing into a hiding monster and hiding under the gold.
- "Hey! Who left that orange in here?"
- You were polymorphed from eating a mimic corpse while hallucinating when the guard entered.
- See the encyclopedia entry for human.