It would appear that few people remember the Sentry. There are no records of his existence or any tales of his exploits. The only person who remembers him is Reed Richards, and he only has vague memories of a hero he once called a friend. There are records of a Robert Reynolds however, and Reed has tracked him to the S.H.I.E.L.D. Raft facility. Reynolds apparently approached S.H.I.E.L.D., claiming to have killed his wife, and wished to be incarcerated.
The exact powers of the Sentry are unknown and it is unclear why there are no records or memories of his time as a hero. Reed Richards recalls him being extremely powerful but has no further information available at this time.