The Walrus Herd is a group of Walruses inhabiting Walrus Island, of which Rotor Walrus, one of the main members of the Knothole Freedom Fighters, is a part of along with his family. They inhabit the Northern Tundra as the most influential species of Mobians in that area, where they inhabit the city of Iceborough. Both the original Dr. Robotnik and Dr. Eggman have menaced them on multiple occasions, prompting the Freedom Fighters to come to their aid.
Threatened by the Robotniks
Herd member Sherman Walrus was a known operative of the Kingdom of Acorn during the Great War. His son Rotor Walrus later took up residence in Knothole following Dr. Ivo Robotnik's takeover, evacuated there by the Original Freedom Fighters. He would subsequently become one of the founding members of the Knothole Freedom Fighters. (StH: #77, #142, #143)
The rest of the Herd either remained or evacuated to their home in the Northern Tundra, where they lived peacefully until Robotnik detonated a Neuron Bomb over the region, allowing him to brainwash the Walrus Herd into serving him. They were to be used in a scheme to freeze the entire planet, but the efforts of Rotor and two members of the Arctic Freedom Fighters set them adrift on an iceberg. Later, the effects of the Ultimate Annihilator freed the Herd from this control, allowing them to live peacefully for some time. However, Dr. Eggman soon made his first foray into the region, placing the Herd under his control and driving Rotor-who had returned to spend time with his family-out of the region. Fortunately, the Arctic Freedom Fighters were able to get him to safety, though the Herd remained in Eggman's hold for the time being. (StH: #31, #32, #72, #85)
The Knothole Freedom Fighters eventually returned to the region, using the magical Sword of Acorns to free the Walrus herd from Eggman's grip once again. Following this, they entered a period of peace, and their city of Iceborough became a prominent area of the region. (StH: #109, #215)
Dark Egg Legion
The Arctic Freedom Fighters later contacted New Mobotropolis to inform them that a chapter of the Dark Egg Legion had captured the Walrus Herd. Sonic the Hedgehog was dispatched to aid the team in freeing them, and learned from them that the Legion had constructed a Psionic Emitter to aid them in using their sonar abilities to once again brainwash the Walrus Herd. The enslaved Walruses were employed in maintaining the Legion's new base above water, and a horde of them armed with spears, axes, maces, and swords stood guard as the Freedom Fighters arrived to liberate them. (StH: #214, #215)