Vulcans are massive God-like beings who possess unmatched power over Demons, fire, chaos, and destruction. They are very hostile towards Humans, and act as tyrants over Demons of any kind.
For a Human, Demon, Part-Human, Elf, Dwarf or any other mortal, it is impossible to kill a Vulcan. This is due to their direct ties to the Underworld. Their weakness lies only with the Underworld, so any item made there, or enchanted there will be able to kill one. They are, however, immensely powerful and even if you are correctly prepared, it'd be near impossible to damage it. Their natural resistance to every form of damage makes them the perfect super-soldier. However, killing them is highly recommended due to the loot that can be had. Rare metals, ancient scrolls, and often they have multiple Souls, since all Demonic creatures have the ability to steal Souls. This is how they become so powerful.
Vulcans rarely involve themselves in the affairs of mortals. This is because they've acheived a higher understanding of the realm around them. They spend most of their time researching subjects they deem worthy.
They also take pleasure in torturing Humans, and then using them as their minions, giving them eternal life. In return, the Humans are forced to live eternally under the rule of the Vulcans.
They often compete with Dragons and other powerful beings such as Behemoths, Wyverns, and Wolves. They usually get in boasting matches with them, claiming to be the superiour being, right before getting into a violent fight.
When speaking to a Demon, Demons will often complain about Vulcans being annoying, tyrannical, and greedy. They are by far one of the more violent and truly evil beings in the Realms.