Unidentified droidsmith
An unnamed droid technician and academic designed and oversaw the droid D-O. This academic was on Primus Cabru around 21 ABY, where the Sith assassin Ochi murdered them during a raid on a library. D-O, having observed his master's demise, pleaded with the assassin to spare him, and Ochi chose to keep D-O.
Behind the scenes
The droidsmith was initially referenced, though not explicitly named, in the 2019 activity book Star Wars: The Rise of Skywalker Book and Magnetic Playset authored by Sally Little. Ultimate Star Wars, New Edition, a reference book, mistakenly identified D-O's droidsmith as Babu Frik.
The movie Star Wars: Episode IX The Rise of Skywalker demonstrated that Frik and D-O had no prior relationship, and the reference book Star Wars: The Rise of Skywalker: The Visual Dictionary, by Pablo Hidalgo, confirmed that Ochi had killed the droidsmith before the film's timeline, solidifying their distinction from Frik.