"Even other monsters fear him, so expect a clobbering. He shrugs off explosions. Good luck."
— Quake Manual
In Quake, a Shambler is a large yeti-like beast with a blood-stained shaggy coat, a very large mouth displaying enormous fangs, no visible eyes, and sharp claws. The Shambler has a complete lack of facial expression. Its furious melee claw smash does enormous damage, and at a distance, it can attack by projecting a bolt of electricity towards its opponent. Its electric attack will only work if it sees its enemy when it ends its charging up animation. Otherwise, it'll miss.
The Shambler is a very intimidating creature, and not just for its menacing appearance. Despite having a large frame, it is surprisingly fast and difficult to outrun. Its electric attack can take up to 30 health points (40 on Nightmare difficulty), and it will hit unless you're hiding behind something or are outside of its range. Because of its size, it'll try to clobber you with its melee attack if you're even a moderately short distance away; this can take up to 60 points of damage in a single attack (up to 120 in dual-hand claw). And with a total of 600 health points, the Shambler is the toughest Enemy to kill in the entire game.
Since the Shambler takes half damage from explosives, avoid using the Grenade or Rocket Launcher against it. Instead, take out your Super Nailgun or your Thunderbolt and fire away. Both of these weapons will take out a Shambler in no time. The ordinary Nailgun is slightly less effective against the Shambler, as it only takes 7 health points of damage instead of the usual 9.
Taking cover a safe distance away is probably the most advisable strategy when dealing with a Shambler. If it can't see you while using its electric attack, it will miss. An alternative method is to get up close to the Shambler with either your Shotgun, Double-Barrelled Shotgun, Nailgun, Super Nailgun, or Thunderbolt equipped, dodge its melee attacks, and shoot at it until it dies. This is a very risky maneuver, but an efficient way of handling the creature without taking damage when done successfully. But if you are chased by one of these, it's a good way to defend yourself. However, this strategy is only for one-on-one combat, and could cause serious problems if attempted while in the company of several other enemies. Also, avoid this technique if playing on Nightmare difficulty; its attacks are twice as fast, and getting too close for even a second will likely cause considerable damage, and you are likely to be killed before you kill it.
Try not to get cornered, if this happens, your last resort to survive is blast it with Double-Barrelled Shotgun or Super Nailgun as much as you can, hopefully it will die before you are ripped to shreds.
With other enemies, the threat posed by the Shambler becomes all the more significant. Because of how quick its electric attack animation is, you probably won't notice it charging up until it's too late. A good idea is to try and isolate the Shambler so that you can manage it without dealing with constant distractions from all around you. Depending on its position, you can either lure it away into another room and kill it first, or you can lead the other enemies off so as to take them out one at a time before turning your attention to the Shambler. As usual, pound it with your Super Nailgun or Thunderbolt, and it'll be down in no time. If you want to take a risk, you can pull out your Nailgun or Super Nailgun and find a place so the Shambler won't see you. Run out and shoot a few Nails, then run back in. If you keep performing this move, you'll confuse it. This strategy is only for experienced players, one misstep can be lethal.
A Shambler can mow down any other monster in an in-fight, but it's hard to have its lightning attack intersect with another creature. It is actually a better approach to provoke it with enemies that have long-range attacks, such as a Vore, a Death Knight, or a Scrag. While risky, causing an in-fight with a Shambler can be an incredibly useful approach when done correctly.
The Shambler is one of only five monsters (along with the Vore, Wrath, Spike Mine's explosion, and Spawn's death explosion) that are capable of gibbing the Zombie (usually with its dual-hand claw attack).
According to John Romero, Shamblers lack eyes because the fantastic realms that they’re native to are dim, humid, and horrific, thus eyes would be unnecessary. In the same paragraph, he also confirmed that they have shaggy coats.
Because of its infamous penchant for teleporting into areas and being named 'Shambler', it's logical to assume that this monster was directly inspired by Dimensional Shamblers, creatures created for the Cthulhu Mythos by H.P. Lovecraft. Just like the enemies in the game, the Dimensional Shamblers could teleport between worlds. The Shambler has the nickname of "Dark Young".
The Shambler also appears in RAGE, in the form of an easter egg. There, it appears in the secret Quake Room, in the form of a "Shambler Plush".
Fan-made Shambler in Doom 3 has similar appearance to Hell Knight.
↑Interview with John Romero where he states, ‘You're right about the eyes - most of the monsters don't have them. The world of Quake is dark, wet and scary and they didn't really need em. The Shambler is supposed to have a shaggy coat.’