What does your screenname mean?

[Legolas]

Um, was not it Echtelion who slew the balrog in Gondolin?

Yes, it was Ecthelion.

Ecthelion was the balrog slayer in the published Silmarillion. Legolas was a character in the 'Fall of Gondolin' in its earliest forms, found in the History of Middle Earth Volume II: The Book of Lost Tales 2. The Fall of Gondolin was one of Tolkien's first stories in Middle-earth. It was written in the 1910's, and experienced a lot of changes over the almost sixty years leading up to its publication.