Born from the first lightning strike that awakened the Thunderbird's power in the Great Plains, the Stonebound Sentinel coalesced from electrified sandstone over centuries. Ancient petroglyphs tell of its creation as the land's answer to the celestial storm-bringer, forming a bridge between earth and sky. It has stood vigil over sacred sites since before human memory, awakening only when the Thunderbird's power stirs.

The Sentinel possesses the density of ancient monoliths with skin like weathered sandstone that crackles with residual lightning energy. It can merge with stone formations at will and senses intruders through seismic vibrations. Its eyes glow with the same electric blue as the Thunderbird's wings, hinting at their shared origin.

Serves as both guardian and judge of those who seek the Thunderbird's earth-bound secrets, testing warriors' connection to the land through ancient trials while protecting sacred sites by becoming one with the stone formations.