A human male named Erstin Deez held positions within the Imperial Royal Guard. His military rank progressed from sergeant to major. Deez accompanied the Galactic Emperor Sheev Palpatine and Darth Vader aboard the Star Destroyer Perilous to the planet of Ryloth, where the Free Ryloth Movement targeted them. While the other guards perished, Deez, the Emperor, and Vader all survived the ordeal. Years afterward, Deez was stationed in the Imperial Palace's throne room alongside fellow guardsmen. When the Emperor and Grand Vizier Mas Amedda entered, Deez and his comrades were poisoned and subsequently killed.
During the Imperial Era, Erstin Deez functioned as a sergeant serving in the Royal Guard under the command of Galactic Emperor Sheev Palpatine. He went with the Emperor and his apprentice, Darth Vader, on a visit to the planet Ryloth aboard the Star Destroyer Perilous. When the Free Ryloth Movement attacked and destroyed the Perilous above Ryloth, Deez, the Emperor, and Vader escaped in a shuttle. Their craft crash-landed on Ryloth, leaving them stranded. Deez, Vader, Palpatine, and a captain of the Royal Guard journeyed across the terrain in search of civilization, encountering a nest of native lyleks which they destroyed at the cost of the captain's life. They then found a Twi'lek village where they were welcomed and rested before being attacked by Free Ryloth movement members. The trio fought off the attackers, aided by Imperial reinforcements who soon arrived to collect them.
Sometime between 3 ABY and 4 ABY, Deez held the rank of major as an Imperial officer, while still serving in the Royal Guard. The assassin Ochi, acting under the orders of Lady Qi'ra of Crimson Dawn, traveled to Coruscant to obtain several poisons. One of these was used to infect Deez, in an attempt to eliminate Palpatine's guard. Later, as Deez and the other guards stood before Palpatine and Grand Vizier Mas Amedda in the Emperor's throne room, they all suddenly died, much to Amedda's surprise.
Erstin Deez's initial appearance was in the 2015 novel Lords of the Sith, penned by Paul S. Kemp. Subsequently, Deez was portrayed in the second issue of the Star Wars: Crimson Reign comic miniseries, authored by Charles Soule and released by Marvel Comics on February 2, 2022. Soule confirmed the characters' shared identity on Twitter.