The Balrogs
Balrogs were spirits made from fire, they were mainly a shadow, and always carried a whip with them. Though in Bereiand, most were destroyed in the destruction, and hid under the Caradhras, where they were released by the Dwarves of the Khaza-dum, and got loose, so the mines were named Moria, the Black Chasm. The Balrog here was destroyed by Gandalf, when the Balrog took a step forward, the bridge fell, though brought Gandalf the Grey down with him, but Gandalf did kill the Balrog here, but Gandalf himself came back as "Gandalf the White."  These Balrogs were known as the Dark Enemys, and Valaraukar, by the high elvens.