The current head of the Assassins' Guild. He succeeded Dr. Cruces after his death; before that he was his deputy. He is a kindly looking, distinguished old gentleman with white hair, eminently professional and seemingly unflappable. Certain evidence suggests, however, that he was not always quite as intelligent or in-control as he is now. He was at school with Havelock Vetinari, where he was a bully and something of an imbecile, with a propensity for calling everyone scags, including Vetinari, whom he also referred to as dog-botherer. Thirty years' passage seems to have improved him.

Allegedly, Lord Downey's preferred method of inhumation is poisoning, though no deaths have yet to be attributed to him. Pratchett suggests this is probably due to the fact that he is very good at his job. His special recipe for humbugs, submitted to Nanny Ogg, calls for "arsenic to taste", though, since arsenic is actually very traceable, this is likely a slight bit of misinformation on his part. One current tradition he maintains is inviting certain students to his office for sherry and an almond slice. Given the nature of most Assassins' Guild traditions, this could be seen as a kind of impromptu "pass or fail" examination (see bitter almonds for the reason why).

Lord Downey first appears in Men at Arms, makes his first appearance as Guildmaster in Feet of Clay, and appears again in Hogfather. He also appears in Night Watch as a student bully. In the Sky One adaptation of Hogfather Downey was played by David Warner.