Grendahl, a Captain, served as a fleet officer within the Imperial Navy.
During the year 5 BBY, Grendahl served aboard the Star Destroyer that took Adalric Cessius Brandl into custody for a short time following his act of going rogue. After the Kierra, the vessel Brandl was on, was seized, Grendahl was the initial officer to conduct an interview with Brandl. Furthermore, Grendahl was the one who initially told Brandl of their impending rendezvous with the Interrogator. Following this, Grendahl proceeded to question Thaddeus Ross. After determining that no significant violation had occurred, he communicated to Ross that he was to be given 10,000 credits as a reward for his assistance in capturing Brandl. Concluding the interrogation, Admiral Etnam advised Grendahl that Brandl himself would be tasked with escorting Ross back to his own vessel. Grendahl was quite surprised by this order, yet he followed the instructions of his commanding officer.