Written and created by Paul Jenkins, The Sentry first appeared in this series that was being run under Marvel Knights. It told the story of a seemingly normal man named Bob Reynolds who wakes up one night remembering that he had once been a superhero, and his arch-nemesis, The Void, was coming back to destroy the world. Bob drinks the super serum that he had hidden in his home, and becomes the Golden Guardian of Good once again. He travels to meet up with his old allies, tries to get them to remember him, and rally them together so they can fight the coming threat of the Void.
The Sentry: Reborn - This is a graphic novel that reprints the second Sentry mini-series from 2005. This is another mini-series that follows the adventures of the Sentry after being part of the New Avengers and trying to learn more about his past. I won't go into more detail because I would be giving away some important plot details but if you're craving for more comics featuring good ole' Sentry then I recommend picking this up and it does have an interesting twist concerning both the character and "The Void" in the second half of the mini-series.