The Demon Knights is a team created by writer Paul Cornell for the series of the same name. The team is described to be part of the medieval time period within the DC Universe, having distant connections to the post- Flashpoint DC Universe in the present. Cornell described the team as being reminiscent to media works like the video game Dragon Age and TV series Game of Thrones.
Most of the team first came in contact with each other by chance in a small farm village pub, where Jason Blood, Madame Xanadu and Vandal Savage have a beer together, suggesting they've all met before. Shining Knight, Al Jabr and Exoristos are all patrons of the pub at the same time, when it's attacked by the Questing Queen's Horde of dragons and dinosaurs, forcing the six of them to defend themselves.
Later in modern day time, in the first issue of Stormwatch, also written by Paul Cornell, the Scourge of Worlds invades Harry Tanner's mind, finding that the Stormwatch team is centuries old, with its earliest incarnation being that of the Demon Knights, including Etrigan, Vandal Savage, and Madame Xanadu. A younger Merlin calls The Demon Knights his Stormwatch. The Demon Knights disperse and are retrieved by Al Jabr because of the vampires marching towards Al-Wadi in Moorish Spain. The vampires are stopped by The Demon Knights. Extorsis who had located The Black Diamond and had held on to until she placed it in Al Jabr's vault within a locked chest. Al Jabr keeps the Black Diamond beside The Holy Grail which cancel each others powers.