Warning: This article contains spoilers for Annihilation: Scourge #1, by Matthew Rosenberg, Juanan Ramirez, Cian Tormey, Federico Blee and VC's Cory Petit, on sale now.
Marvel's Annihilation event series follows a series of apocalyptic invasions primarily dealing with the cosmic side of Marvel. In 2006's Annihilation First, Annihilus led the Annihilation Wave into the universe. In 2007's Annihilation: Conquest, Ultron attempted to assimilate the universe into the Phalanx.
Now, Annihilation: Scourge Alpha #1 kicks off the the latest round, this time with the the undying legions of the Cancerverse invading and starting their assault in the Negative Zone, where they decimate the combined forces of Blastaar and Annihilus.
The biggest threat comes from the Revengers, the Cancerverse version of the Avengers. While the original leader of the Revengers, Lord Mar-Vell, appears to still be dead after the events of Thanos Imperative, the remaining Revengers have either returned from death or managed to survive. However, they've picked up a new leader in the form of one of the most powerful beings in the Marvel Universe: The Sentry.
The Sentry has a long and turbulent history in the Marvel Universe. Starting out as a drug addict after another fix, he chanced upon an evolution of Captain America's Super-Soldier Serum that granted him the power of a million exploding suns. He debuted as one of the most powerful superheroes ever, but brought with him the terrible Void, a ruthless dark shadow that could match his power and twisted its way in the hero's mind. With the help of Doctor Strange and Reed Richards, Sentry erased all memory of himself to seal the Void away. However, that didn't stick, and the Sentry eventually returned to the world of heroes.
The Sentry joined the Avengers, then the Dark Avengers under Norman Osborn, and was finally killed after losing control of and merging with the Void during the Siege of Asgard. But as you might have guessed, that didn't stick either.
After Sentry was brought back to life by the Apocalypse Twins to become one of their Horsemen of Death, his already fragile mental state continued to deteriorate, and he began to consider himself an heir to Apocalypse himself. However, he helped the Avengers defeat the Celestial Exitar the Executioner and decided to fly far off into space to dispose of the body.
After Doctor Strange eventually found him and freed him from Apocalypse's influence, the Void was inadvertently freed too. Sentry returned to the mindscape, and tried to live a life as a hero within it in order to contain the Void. Unfortunately the Sentry's efforts were sabotaged, and the Void was once again released. Sentry merged with Void once again, and flew off into space.
Recently, the Sentry resurfaced in Black Panther and the Agents of Wakanda. After Thor softened him up, Fat Cobra performed an exorcism of sorts on the Sentry, seemingly removing the Void and promptly eating it. After that, a clearly distressed Sentry flew off to an unknown destination in space.
In Annihilation Scourge Alpha #1, the Cancerverse invasion is being led by the Sentry. Even though he's seemingly freed from the Void's influence, he's apparently gained a brand new level power by joining with the Cancerverse. Since he was already one of the strongest beings in the Marvel Universe, this power boost makes him even more terrifying. With an equally intimidating army at his back, the Sentry is set to give Marvel's cosmic heroes one of the biggest challenges they've ever faced.