Hellhounds are supernatural canine beasts and are antagonists that appear in the TV show Supernatural. They are supernatural demonic dogs, or pit bulls, from Hell. They have been described as being terrifying and have have been feared by humans, demons, and even angels.
Crowley states that after god created the universe he created lots of creatures including hellhounds. The beasts were created so the almighty can have friendly companions. Whereas dogs are man's best friends hellhounds were supposed to be god's best friend. However, hellhounds turned out to be exceedingly dangerous and vicious to the extreme, so god deemed them to be destroyed. But Lucifer, who was cast out from heaven and made his new residence on earth, managed to save one hellhound named Ramsey, who was pregnant with hellpup litters. From Ramsey and Lucifer's protection hellhounds population regrew. Ever since then hellhounds serve demons from hell, collecting souls of humans who made deals with the unholy beings when their due came.
Hellhounds are cunning, voracious and tenacious to the extreme: once a hound has the scent of its prey, it will hunt down its prey for life and will never stop the hunt until it or its prey is dead, or unless its master calls it off. Hellhounds will often physically rip their victims to shreds in order to collect their souls. However, their mere presence is enough to literally scare most people to death. Other times, the victims will be driven crazy and commit suicide. They are clever and capable of being improvisation, so fooling or distracting hellhounds are very difficult. Their sizes vary: some are small, others are large (ranging from standard dogs to that of akin to colt or calf).
As dogs, they are loyal and answer only to demons they serve; they cannot be swayed or bargained with. Not even Crowley could devise a way to throw them off, short of using a bigger hellhound of his own to kill them. Exactly how they are controlled is unclear.
Any demons can command a hellhound, but very few of them can truly tame one, let alone taming many at the same time. It is unknown if any demons, or angels for that matter, could overpower a hellhound without the use of certain weapons. However, an archangel could easily destroy one. Crowley keeps a hellhound as a pet. This hellhound is bigger than most other hellhounds and Crowley uses it to fight off another, smaller hellhounds. Only Lucifer can command the mother of hellhounds, Ramsey.
According to Supernatural: War of the Sons, Hellhounds were made by Lilith but this is Non Canon.