<P> Tolkien tells of two Balrogs slain by Elves in the fall of Gondolin . During the assault on the city, Ecthelion of the Fountain fought Gothmog, and "each slew the other ." Glorfindel fought a Balrog who waylaid an escape party from the fallen city; both fell from the mountainside in the struggle and perished . </P> <P> In the War of Wrath that ended the First Age, most of the Balrogs were destroyed, although some including the Balrog known as Durin's Bane, managed to escape and hide in "caverns at the roots of the earth". </P> <P> In The Fellowship of the Ring, the Fellowship ventured through Moria and were attacked in the Chamber of Mazarbul by Orcs and the Balrog . Gandalf faced the Balrog at the Bridge of Khazad - dûm and broke the Bridge, but was dragged down by the Balrog . He slew the Balrog but perished himself at the same time--to be sent back as the more powerful Gandalf the White . </P> <P> Tolkien's conception of Balrogs changed over time . In all his early writing, they are numerous . A host of a thousand of them is mentioned in the Quenta Silmarillion, while at the storming of Gondolin Balrogs in the hundreds ride on the backs of the Dragons . They are roughly of twice human size, and were occasionally killed in battle by Elves and Men . They were fierce demons, associated with fire, armed with fiery whips of many thongs and claws like steel, and Morgoth delighted in using them to torture his captives . They were loyal to Morgoth, and once came out of hiding to save him from capture . </P>

Who does gandalf fight in the fellowship of the ring