In the Fall of Gondolin Gothmog was finally killed by Ecthelion, who was mortally wounded in the process.
His successor among the seven Balrogs was Durin's Bane, an extremely powerful Balrog, almost as powerful Gothmog, as he was able to expel the Dwarves from of Moria and even able to cast a counterspell on Gandalf, almost killing him. He gained his name because he was the one who slew Durin. Durin's Bane was finally slain by Gandalf, who was travelling with The Fellowship of the Ring. Gandalf knew that Durin's Bane was far too strong for the others, so he challenged The Lord of Balrogs in a single battle, in which they both died but Gandalf was returned to life by the Valar or Eru Ilúvatar.