Dead Matrix

Let the sunshine, let the sunshine in, let the sunshine in.

The Dead Matrix is carried within the chest of Nemesis Prime.

Originally one of many Autobot Matrixes of Leadership from a mostly undocumented corner of the multiverse, it was corrupted over time inside of a defeated Prime. As the body lingered, eventually very little of Primus' essence remained inside. Using Nemesis Prime, Unicron's tortured clone of the fallen Prime, Unicron was able to insert a portion of his own dark essence into the artifact. This newly created weapon would be able to kill Primus should it ever be opened in his presence.

From Teletraan I: The Transformers Wiki, a Wikia wiki.