Klaus is a BossMonster exclusive to Don't Starve Together, introduced in A New Reign. He resembles a larger version of Krampus. He spawns after a player puts a Deer Antler in a Loot Stash, which will return Bone Shards due to it being an incorrect key. He spawns with one red and one blue Gem Deer. Killing any of these deers, or if they are away by 30 units, will enrage him, increasing his damage, health by x2.744, takes 64% less incoming damage, and increases his size. He is also able to spawn 2-6 Krampii during the fight. Using the Telelocator Staff on him is not a viable way of isolating him from his Deer, as he will get enraged when separated from them even if they are still alive.
After killing him, he will be revived, losing the chains around his body, allowing a large mouth from his stomach to gain a new long-ranged "chomp" attack.
Once he's killed again, he will drop Charcoal, a Monster Meat, and a Stag Antler which is the proper key to use on the Loot Stash. Opening the Loot Stash will yield 4 Bundled Supplies. If the Gem Deer are still alive when he's killed, they will turn into normal No-Eyed Deer, dropping their corresponding gem. It is worth noting that during Winter's Feast, Klaus is present year around, and no longer provides bundled supplies, instead 6 gift boxes.
During the Winter's Feast event Klaus has a slightly different appearance. His horns turn white with red stripes, and his chains are golden.
The name Klaus is a short form of Nikolaus, referring to Saint Nicholas, the historical origin of Santa Claus.
Even though he is blind due to his eyes sewn together into a single large "X" shape, it is possible that Klaus has a keen sense of smell to track down the player. This is supported by Klaus occasionally attempting to "Sniff out" the player. This is also confirmed by Wickerbottom's examination quote.
Klaus is the first boss to have two different boss battle themes, the second being the Ancient Fuelweaver. Its second theme plays when Woven Shadows are being summoned.
When preparing for the "chomp attack", Klaus looks a bit similar to The Screecher, a creature from the horror mod of the same name made by Klei Entertainment.
When put to sleep, Klaus covers his eyes for some reason.
Klaus seems to be wearing the old version of the Life Giving Amulet, as evidenced by its octagonal shape.