Red Court vampire

Red Court vampires are one of three types of vampires. They are first mentioned in Storm Front.

Description
Red Court vampires were non-human creatures, capable of disguising themselves as humans and preying upon humans for their blood. A lot less human-like than White Court vampires, they are slimy bat-like creatures hidden under a flesh mask, which they use to trick their prey into being more comfortable, and to hide in plain sight.

They are incredibly strong and fast, and can heal from any injury quickly. They are, however vulnerable to sunlight and to having their bellies cut open, which can spill the blood they have drunk, seriously weakening or even killing them. Crosses and other forms of faith magic don't repel them as much as they do Black Court vampires, and they have a more solid footing in reality. Because they are more magical than humans, crossing a threshold is dangerous for them, potentially leaving them nearly paralyzed.

Their saliva contains a potent magical narcotic, which gives the prey a euphoric feeling. It is highly addictive, allowing Red Court vampires to control their victims rather easily. The narcotic lowers the victim's inhibitions, dulling the pain of the vampire's bite. Addicted humans have been shown to go to great lengths to protect their vampiric masters, and willingly provide information from the mortal community as needed. Susan Rodriguez calls it the Kiss, stating that half-vampires have in their saliva a less potent version of it than full vampires.

The oldest of them can wear any flesh mask they wish and can go around in the daylight hidden from the sun in the shadow of their own mask. This is something the White Council didn't know until Martin told Harry Dresden.

Also called esclavos de sangre, blood slaves were completely feral vampires. Almost like animals, they could not create a flesh mask, and were considered scum and occasionally used as expendable cannon fodder.

Transformation
The Red Court vampires are also capable of transforming ordinary humans into other vampires in a two-step process: the human will initially be infected with the vampiric thirst for blood, completing the transformation into the demonic form at a later time when they feed on a victim for the first time.

Infected humans with sufficient strength of will are known to refrain from feeding for an indefinite length of time, but no cure has been found for their state before the Red Court's destruction.

It is implied that the Faerie Queens, or beings of similar power, can or completely destroy the vampiric infection with a magic known as an Unraveling. The hunger for blood makes controlling their emotions very difficult and very easy to lose control in any situation where emotions run high.

Storm Front
In Storm Front,

Grave Peril
In Grave Peril,

Death Masks
In Death Masks,

Changes
In Changes, "Esclavos de Sangre", Blood Slaves—feral vampires—are sent to be expendable cannon fodder to meet Harry Dresden's spellwork. Harry and his team were expected, and there was no element of surprise.

Near the end of Changes, Harry Dresden kills Susan Rodriguez, who was the youngest member of the Red Court. In doing so, he completes a bloodline curse, which flows to all other Red Court vampires, killing them and all the half-breeds.