This fell creature was one of the last of its kind, for it is certain that although Morgoth may have won the loyalty of many of these dread Spirits of Flame in the earliest days, many were destroyed in the wars against Elves and Men. Also, there are some among the Wise who claim that there were never very many of them:"No more than seven,"was the opinion of one old sage. Yet Balrogs, unless slain by some mighty force, are immortal, as they are true Maiar, lesser beings of the kind that made the Dwarves and caused the stars to shine. Little wonder, then, that they command such power and such awe. The powers and abilities of Balrogs are legion: they can fly; their force of will and their very presence is so great that all must quail before them, if only for a moment in the case of the valiant; they can wield a weapon in either hand so that each strikes as if wielded by a gigantic Master of Arms; they can seize control of a foe's will and mind, forcing him to do their bidding or shattering his mind beyond repair; they can burn with a fire as fierce as that of a volcano under almost any conditions, and only total immersion in a large quantity of water can douse the flames, which immediately rekindled as soon as the Balrog reaches a drier environment; they can throw certain spells with the skills of the most powerful Magician. Their specific areas of spell mastery are those of fire (of course), detection, and contacting other evil spirits and beings. Balrogs' thought processes are not for the mortal and basically Good to fathom, but it is known that they are fiercely loyal to the Black Foe of the World and that they have long memories for spites and insults against him.
They are immensely proud and have a certain aesthetic bent that reveals itself whenever they have the opportunity to be in charge of constructing a fortress or other building. The throne room of the Balrog of Moria is a good example: a vaulted cavern is lit from above by the eerily beautiful flickering of living flame from the heart of the world and furnished with columns in the shape of flaming Dragons (one of the few other types of creatures that Balrogs respect)and arching red bridges of the magical glass called laen. Spirits of Fire, the Balrogs display the character and power of the most fascinating of destructive forces in every facet.
Tolkien's late statement that there were no more than seven Balrogs, equivalent to the seven princes of Hell in in Christian demonology, contradicts the earlier depiction of the Balrogs, as there was a far greater number of them in the book of lost tales and even the published silmarillion.The discrepancy has been solved by most game masters by assuming that there were only seven True Balrogs but there was a far greater number of lesser Balrogath, minor Fire-spirits who were only the servants of the seven Balrog Lords.