As the superior specimen of the advanced Exin species, Grzax was granted an unusual amount of autonomy after being infected by slag. Though connected to the Hive mind, Grzax retained his personality, much like William Slade.
The Exin race has a natural resistance to mutation, but they are just as prone to infection and mind-control as humans. When the slag brain was destroyed on Krozox, many of the Exin went completely mad due to fractured minds. This led to plenty of confusion regarding the relationship between slag and the Exin.
After the destruction of his command ship and the local slag "brain", many of the Exin went mad due to the severed hive connection. Grzax retained his sanity, but struggled to lead his troops. He was eventually killed during a skirmish with TCF forces.