DT-L21 was a death trooper who was stationed on the planet of Lothal. The Spectres of the Rebel Alliance inadvertently revealed themselves at Old Jho's Pit Stop while on a mission to gather intel regarding a new prototype variation of the TIE/d "Defender" Multi-Role Starfighter. Consequently, DT-L21, along with Baron Valen Rudor, attempted to apprehend the rebel group. Accompanied by a squad of stormtroopers, DT-L21 pursued the Spectres through the subterranean sewer system of Jhothal. Nevertheless, the Spectres successfully linked up with Lothal resistance group leader Ryder Azadi.
During the Galactic Civil War, DT-L21, a human male, served the Galactic Empire as a death trooper. In the year 1 BBY, he found himself stationed within the city of Jhothal on Lothal, a world situated in the Outer Rim. Alongside a contingent of stormtroopers under the command of Baron Valen Rudor, he was present when a rebel cell known as the Spectres infiltrated the planet. Their objective was a rendezvous with resistance leader Ryder Azadi. The rebels attracted Rudor's attention during their operation when Imperial TX-225 GAVr "Occupier" combat assault tanks destroyed the speeder they planned to use for escape. This forced them to seek refuge in the cantina where DT-L21 was stationed. As he, Rudor, and a group of stormtroopers moved to investigate, the Jedi Padawan Ezra Bridger cleverly misled them into believing the rebels remained outside. Eventually, DT-L21 discerned Bridger's deception and directed his forces toward a sewer access point. The trooper inquired of Rudor whether he was aware of its sealed status, to which the pilot responded that he wasn't. The death trooper, confident that the rebels had limited hiding places, deployed dwarf probe droids and stormtroopers into the sewer system.
Despite his best efforts, the rebels succeeded in destroying the probes. Upon receiving this information, DT-L21 issued orders for all troops to converge on the rebels' last known location. He also directed a squad to secure the Outer Town Junction to prevent their escape, while he himself entered the tunnels. In spite of these measures, the rebels managed to flee Jhothal and successfully met up with Azadi outside the town.
DT-L21, a human male, possessed a mechanical-sounding voice. He displayed a distinct lack of respect for the citizens of Lothal, evident in his forceful shoving of Bridger as he proceeded to engage in battle. He demonstrated determination to prevent the rebels' escape from Jhothal, although he was ultimately unsuccessful in stopping them.
In his capacity as a death trooper, DT-L21 was equipped with standard death trooper armor and carried an E-11D blaster carbine. While his voice wasn't scrambled, it's reasonable to assume he had a scrambler integrated into his armor, as was customary for death troopers.
DT-L21 made his initial appearance, though unidentified at the time, in "The Occupation," which was the fifth episode of the fourth season of the animated television series Star Wars Rebels. The episode was released on October 30, 2017. Steve Blum provided the voice for the character, who was credited as "DT-L21."