BD-1 is a small bipedal exploration droid — a "buddy droid", which is what the designation stands for — built to accompany the Jedi archaeologist Eno Cordova. He is introduced in Respawn Entertainment's Star Wars Jedi: Fallen Order (Electronic Arts, 2019) and returns in Star Wars Jedi: Survivor (2023).
Mechanically he is the games' entire toolkit: he scans, he stims, he slices doors, he carries Cordova's holographic records, and he does all of it from the player character's back. The design solves a real problem — a lone protagonist needs someone to talk to — without giving the player a second body to protect.
Narratively he is the inheritance. Cordova left BD-1 in a tomb on Bogano with the location of a Jedi holocron, and the droid spends the first game deciding whether Cal Kestis is the person the recording was left for. The games are about a survivor of Order 66 working out whether the Order is worth rebuilding, and the droid is the piece of it that survived intact.
Canon. BD units postdate the 2014 reset and have no Legends counterpart.