Origin

Star Trek Canon Special Note
Not everything listed in the origin is Canon.  That is because only television shows and movies are considered canon.  This being a comic website there are many things here that are not canon.  So unless it is contradicted in film it should be listed as part of the character biography.    
 
Kaaj is the Klingon Commander of the Varchas.  He is a commander who is bent on strategy and never underestimating his opponent.  When the Federation Captain Christopher Pike out witted him in battle Kaaj swore an oath to get revenge.  
 
Kaaj is also known for his ruthlessness with his own men killing the for even small failures.  Kaaj has even killed his best men.  On one particular mission he used his own assault squad's communicates to barrage them from space in an attempt to kill Christopher Pike.

Creation

Kaaj was created during the series Star Trek: Early Voyages.  He was the Arch nemesis of Pike.  The two would do battle several times in the series but the final face-off never happened as the series ended in mid story.