The name of the immortal beings tasked with protecting a sacred grove in ancient mythology is the Dryads. These tree nymphs are often depicted as guardians of forests and trees, embodying nature's beauty and vitality. In various myths, they are closely tied to specific trees and are vulnerable to harm if their trees are damaged. The Dryads symbolize the deep connection between humanity and nature, highlighting the need for reverence and respect for the natural world.