Born of Blood Lust. 
Redcaps owe their existence to the desire for bloodshed. Should a sentient being commit a vicious act fueled by blood lust in the Feywild, or where that plane touches the world at a fey crossing, one or more redcaps may form where the blood of a slain person seeps into the ground. At first, the redcaps appear to be tiny, bloodstained mushrooms forcing their caps out of the ground. However, when exposed to moonlight, these caps rapidly develop into creatures that resemble particularly small, wizened, and wicked gnomes, with hunched backs and sinewy frames. The creature wears leather pants, bulky iron boots, and a blood red hat. From the moment they are fully grown, they crave nothing but carnage and violence, and immediately seek to fulfill these desires.   Redcaps are as subtle as rabid wolverines. They resort to direct confrontation, and live for the mayhem of mortal combat. A redcap has very little capacity for stealth due to its incredibly heavy, thunderous iron boots. However, when near to potential prey, a redcap can slice through a victim before they have time to react.   Redcap Adventurers.
Redcap adventurers are rare for many reasons. Redcaps would much rather slaughter independently and undeterred by other folk, and they would often rather kill people than cooperate with them. However, a redcap might cooperate with an adventuring party if it finds the benefits of cooperating with the party are greater than the benefits of being alone. For example, the redcap may be able to kill creatures that it could not kill without the help of the party. A redcap might also end up residing in a settlement, whether by its own will or because its territory was invaded or settled upon. If this settlement has a law system, or at least a code of conduct set in place, and the enforcers of the law or conduct for the settlement are powerful enough to overwhelm a murderous redcap (if murder or the like is frowned upon in the community), the redcap may seek out an adventuring career, possibly specifically targeting criminals. A redcap adventurer almost always chooses a life of adventure when it positively affects the redcap's best interest, although upon rare occasions, other factors may come into play.