While not much is said about them within the series, Devil Forgemasters are not mere sorcerers; they are not just trained in black magic, but also in the arts of alchemy and spiritual metaphysics, being able to craft massive weapons and arsenals from mere prime and raw materials of nearly any sort, as well as creating magical living beings with the forbidden knowledge they possess.
Their creations bear the namesake of "Innocent Devils", creatures summoned and born of darkness, ranging from original and self-made, to even the formerly deceased and revived. All created beings hold strict and utter loyalty to their respective Forgemaster and grow in power through battle and destruction.
Their ranks having been in the employ of Dracula himself, may also be responsible for the mass creation of many of the series' enemies and fiends alongside Dracula's and Castlevania's own influence and summoning of evil creatures, although this is mere speculation.
It is also said that the strength of a Devil Forgemaster rivals that of Death himself. Because of this, only few humans are known to be able to use Devil Forgery. Only two are present in the game itself, Hector and Isaac, both of which are identified by a crest or symbol of the Devil Forgemasters (Hector has this on the back of his armor, while Isaac has it as a tattoo).
Devil Forgemasters are known to go only by their first name. While the reason for this has never been explained, it is probable that the dropping of their family name is part of the requirements while studying the black arts, as a way to symbolize their renunciation to any bonds that may still tie them with their past normal lives.
In the Castlevania animated series, instead of manifesting Innocent Devils from pure darkness, the main way both Devil Forgemasters, Hector and Isaac, are able to utilize their magic is by performing rituals with special tools, either to bring people and animals back from the dead or to call demonic spirits from Hell into intact corpses, transmogrifying the bodies and transforming them into creatures of the night in order to enlist these resulting creations in Dracula's army. This appears similar to necromancy on the surface, but Hector explains to Godbrand that interpreting it as such fundamentally misses the point because the goal of forging is to create living beings: "He's not dead. We create life from death here." Indeed, Hector further explains to Carmilla that "night creatures" are species in hiding, able to increase their numbers in nature without the help of Devil Forgemasters.