A group of warrior monks with genetically engineered anger issues served King Hydroflax and acted as his bodyguards. They used their sentient laser swords to threaten the Doctor[which?] and River Song when it was discovered that River was planning to kill Hydroflax and steal the Halassi Androvar that was lodged in his brain. (TV: The Husbands of River Song)
Behind the scenes
These monks were extremely similar to the Headless Monks (also created by Steven Moffat), with their hooded cloaks with blacked out faces as well as their sentient laser swords. However, nobody on the production team has ever addressed these striking similarities.