Gromel was the former commander of the Black Legion, and appeared in The Phoenix On The Sword. He is of Bossonian descent. He is a very large man, described as a "giant".
In The Phoenix On The Sword, he was one of the five main conspirators in the plot to kill King Conan and instate Baron Dion as the new king of Aquilonia. He acted primarily out of a desire to control the imperial army, as well as a hatred for Pallantides, commander of the Black Dragons. Through his connections, he was able to bribe a young officer of Conan's personal guard to lead his men away from Conan's bedchamber at midnight, allowing Gromel and his fellow conspirators (as well as 16 hired rogues) to assassinate Conan while he slept.
During the coup, unlike most of his fellow assassins, Gromel wore a full suit of armor. He carried a sword, and used his massive frame to break down Conan's bedchamber door. However, instead of finding a sleeping and confused Conan, they found him partly covered in armor and baring his long sword. Gromel was the first to charge Conan. However, Conan was able to dodge his charging thrust, and with a single mighty slash was able to kill Gromel, shattering both Gromel's helmet and Conan's own sword due to the force of impact.