Blagg was a lieutenant serving within the ranks of the Imperial Military. This officer found himself stationed within Detention Block AA-23 aboard the Death Star, the Empire's ultimate weapon, in the year 0 BBY. Blagg's duty was to ready the IT-O Interrogator droid for the interrogation of the Princess Leia Organa, and he became quite worried when a critical component was late arriving, just as Grand Moff Wilhuff Tarkin arrived for an inspection. When Blagg commanded the delivery droid, an MSE-6 series repair droid with the designation MSE-6-G735Y, to depart with haste, it bumped into Tarkin, accidentally activating a holorecording featuring the stormtrooper known as TK-421. Tarkin was momentarily distracted by the recording, before returning to scolding Blagg to avoid excuses or shifting blame for the delays. Blagg then inquired whether they should commence the interrogation, but Tarkin responded that Darth Vader would be the one in charge of that.
Blagg made an appearance in the short story titled "Of MSE-6 and Men," penned by Glen Weldon for the 2017 collection From a Certain Point of View. Following the release of the sequel trilogy film from 2017, Star Wars: Episode VIII The Last Jedi, Weldon spoke about a theory suggesting a link between the "broom boy," Temiri Blagg, and Lieutenant Blagg. Weldon stated that he simply created a name that sounded Star Wars-like and had neither been contacted by nor contacted Lucasfilm regarding it.