In Egyptian mythology, the being that guards the entrance to the underworld is Osiris. He is revered as the god of the afterlife, resurrection, and fertility. Osiris is often depicted as a mummified king, symbolizing eternal life. His role is crucial in the judgment of souls, where he determines the fate of the deceased. Additionally, Osiris represents the cycle of death and rebirth, embodying the agricultural cycles of ancient Egypt, further cementing his significance in the Egyptian belief system.