Jack Noir is an Agent of Derse who appears in every session of Sburb. He oversees various affairs of the kingdom and does all of the most important and most tedious paperwork, and is the direct subordinate of the King and Queen. In the kids' session, he slew the Queen, and soon after, the King, declaring himself as the Sovereign Slayer and wreaking havoc on the Medium. Karkat has identified him as the "cancer" he created in the kids' session.

A "Jack" is a face card in a normal deck of cards that ranks below the king and queen, and "Noir" is a pun on the detective film genre film noir, an allusion to Problem Sleuth, and Jack's alternate universe counterpart. "Noir" also means "black" in French, making his full name a pun on the card game Blackjack. (Resemblance to the name Jack Black is just an amusing coincidence.) Bec Noir, the name given to Jack's fully prototyped form, is possibly a play on the French phrase bête noire, meaning "black beast" literally, or used as slang for a pet peeve or something feared obsessively.When he was introduced, Jack appeared to be a normal-looking Dersite wearing a multi-colored jacket with a spade. He particularly despised wearing his jester's hat. Jack Noir was also seen without his outfit on after it appeared to be affected by Rose Lalonde's Prototyping involving the Eldritch Princess, giving it a pink frilly skirt and a hat similar to that of the princess.

Blood Spade Jack Noir
Jack's normal attire.
Jack's role in Derse is to make use of several window-shaped monitors—or Fenestrated walls. He has three such walls. The fourth wall was stolen by Grandpa, and was later seen in his laboratory; Andrew Hussie's study was on the other end of the fourth wall.

Jack can watch events anywhere in the Incipisphere. He views the victories of John and his father over his minions. He seems to consider the monsters they face 'graveyard stuffers'—though, since they're the weakest known Underlings, he's probably right. He is also responsible for keeping prisoners of Derse from escaping, though neither he nor his guards (including the Hegemonic Brute) were able to stop Dad and his massive amount of Mangrit. Dad eventually reaches Jack, and then burns, stomps, and applies shaving creams to Jack's comical hat, after which, Jack heartily sets him free.
Jack finally became so fed up with the ridiculous costumes that he utilized an object in Jade and Jake's present to John (perhaps the Royal Deringer) to kill the Black Queen, taking the ring for himself and ascending to the throne.

Jack Noir is the first major character beyond the four protagonists who the player attempts to name.