When the mentally unstable Mikhail Rasputin flooded the Morlock Tunnels, many were believed dead. However, at the last instant, Mikhail used his powers to open a portal into a parallel dimension dubbed The Hill. In this dimension, time moved at a faster rate, and even though it was a manner of months in the main Marvel Universe, it had been between 10-20 years on the Hill.
The members of Gene Nation reappeared on Earth-616. Their mission was to destroy one hundred humans for every Morlock life that had been lost. Sack and Vessel were the first members to show themselves, killing a number of civilians at a nightclub. Sack had suffocated a coroner and an innocent bystander when the X-Men arrived. They battled with Wolverine, Storm, Cannonball, and later Beast, and were hardly fazed by their show of force. Finding their luck changing, the two Gene Nationals fled.
Later, on the anniversary of the Mutant Massacre, a horrific event in which Mr. Sinister's henchmen, the Marauders, killed many Morlocks, a team of X-Men and the Morlock Callisto confronted an attack group from Gene Nation including Sack, threatening the lives of several civilians by attaching incendiary devices to them that were regulated by Marrow's heartbeat. Seeing it as the only way of stopping the terrorist, Storm ripped out Marrow's heart. Defeated, Callisto took Sack, along with the remaining members of Gene Nation, back to The Hill.
A few months later, Storm was kidnapped by Mikhail and taken to The Hill. Once there she had to fight her way to the top of the hill where Mikhail lived, where she successfully overpowered him. Sack was one of the team that successfully reached the top, yet he had decided to take on the moniker of "Glass". Having won the victory, Storm forced Mikhail to take all of the people living on The Hill back to the real world. In an effort to give the mutants a new start, she settled them in a village outside of her home town in Africa.
Sack was one of the few mutants that was unaffected by the Scarlet Witch's tampering on M-Day, and was next seen on the grounds of the Xavier Institute as one of the 198. He was seen associating with former Gene National Fever Pitch and former Morlock Erg, and almost incited a riot against their Sentinel "protectors". If not for the intervention of Mister M, it could have escalated into a bloody battle. When O*N*E* offered to let the mutants into Salem Center in exchange for being implanted with "tracking" chips, Sack was one of the mutants that had it implanted. When the device's true purpose was revealed he attempted to remove the device, discovering that he couldn't and it was bonded to his skull. Fortunately Mr. M, who did not have one implanted, removed Sack's along with everyone else's.
Utopia and Second Coming
Sack later made his way west, showing up on Utopia where he attempted to take control of a corner of the island before being stopped by Psylocke, Dazzler, and several of the younger members of the X-Men.
Powers and Abilities
Sack is a being composed entirely of a gelatinous body that covers his skeleton. He is able to shift his fluid form to cover and control his host while going about his business virtually undetected. Due to the fact that his body is not made of solid matter, it helps to reduce the pain of physical impact.