The Balrog’s exact size and shape is somewhat ambiguous, with Tolkien’s ideas appearing to have changed over time and from one story to another. Believe it or not, the question of whether a Balrog does or does not have wings is one of the most fiercely debated subjects amongst Tolkien fans. Read the arguments here.
The most probable influence for Tolkien’s Balrogs are the demons of religion and folklore; evil spirits or creatures from Hell. According to some traditions, a demon can be summoned and controlled, which is how warlocks and witches gain their powers. In Christian demonology, some demons are considered to be fallen angels, an idea that resembles the corrupted Maiar of Tolkien’s creation. Demons are often portrayed in artwork in a similar manner to Balrogs, with horns, glowing eyes and bodies made of flame, carrying whips or swords.