0-0-0 — Triple-Zero — is a protocol droid built for etiquette, customs, translation and torture, created by Kieron Gillen and Salvador Larroca and introduced in Marvel's Darth Vader #3, published 25 March 2015. The same issue introduces Doctor Aphra.
The premise is a single, very funny inversion: take C-3PO's silhouette, voice register and obsequious diction, and attach them to a machine whose specialist subject is inflicting pain. The comedy comes from the manners never slipping. Triple-Zero is unfailingly polite while doing appalling things, and the politeness is not a mask — it is the same subroutine, applied.
He works as a pair with the blastomech BT-1, the two of them functioning as the murderous counterparts of the droids from A New Hope. The pairing runs through the Doctor Aphra series from 2016, where the running question is whether Aphra controls them or is simply the organic they have not got round to yet.