A badass character in the Artemis Fowl book series. At the start of the series he is Captain, but is promoted to Major and eventually to Commander. He apparently changed his name to Trouble at his manhood ceremony, having just been accepted into the Lower Elements Police (LEP) Academy. He is Grub Kelp's older brother. Trouble is mentioned throughout the series, and in some books there are a few pages (chapters, in the case of The Arctic Incident) told from his point of view.
"LEPRetrieval One were the best and the brightest. It was every little fairy's dream that one day he would grow up to don the stealth-black jumpsuit of the Retrieval commandos. These were the elite. Trouble was their middle name. In the case of Captain Trouble Kelp, trouble was actually his first name" (Colfer 184).