From Teletraan I: The Transformers Wiki

The Dead Universe is a region in the IDW comics portion of the Generation 1 continuity family

The Dead Universe is a mysterious and malevolent realm that exists beyond the plane of "normal" space. Those who enter are said to become dead in both body and mind and are forced into the service of a vast, dark intelligence. A portal between normal space and the Dead Universe exists in the Benzuli Expanse; it was this portal that swallowed up the first Ark mission. This portal is currently expanding and seems on a path to consume the entire local star system. Beneath the surface of Gorlam Prime, a planet in that system, there exists another such portal—this one taking the form of an immense, ocean-like body of grey material, through which Dead Universe minions may freely travel.

Individuals known to be aligned with the Dead Universe include:

• Nemesis Prime
• Jhiaxus
• Galvatron
• Cyclonus
• Assorted Micromasters
• Nightbeat (subconsciously)
• Thunderwing
• Sixshot