Mordax was an elderly Ratman in the servitude of Ratar-O, Mordax was often beaten by Ratar-O and took out his own abuse on the Thunderian slaves, brutally whipping and beating them. When Lion-O, Panthro, and Pumyra made their move to free their fellow Thunderians from the ratmen's slavery. Pumyra attacked Mordax with the full intention of killing him for his cruelty, but Lion-O asked she spare his life. Mordax later realized the Cats were not his enemy but his master Ratar-O, and retrieved the sword and gauntlet of Omens returning the powerful weapons to Lion-O, who used them to defeat Ratar-O.
A character created for the current Thundercats series
In his first appearance Mordax was clearly someone who was abused and took out his own abuse on others. Though he may have changed, it is still unclear if him helping Lion-O was a true change in character or simply his way of getting revenge on Ratar-O.