Alan Scott adopted the name Sentinel after his ring was destroyed--he found from 50+ years of continual contact with the Starheart, it had mutated him and made his GL powers inherent. Now after some JSA stuff he has his ring back, although his powers are still internalized, he uses his ring to help focus the energies. Last I knew, anyways.
He became the living embodiment of the Starheart, a being of pure energy with just his will and consciousness holding it together.
In Princes of Darkness, Mordru w/ Dr Fate's artifacts, ripped the Starheart from him. Alan turned it back into a ring.