The gothmog zomboid refers to was the lord of balrogs, but he was also killed in the fall of gondolin, so the gothmog leading the army cant be him. balrogs were originally maia, helpful spirits, more powerful than men or elves, less powerful than the gods themselves. the balrogs are corrupted maia, as is sauron himself, who originally served Melkor, the first dark lord. another double name that appears is the name of the elf who killed gothmog originally, he was named Glorfindel. He died at the fall of gondolin in the fight with gothmog. In the lord of the rings a glorfindel helps frodo and company reach rivendell.
there, thats the extent of my knowledge
p.s. a quick edit: wizards were maia i believe, though i havent read enough on it to be sure...