The Giant Squid is an antagonist from 20,000 Leagues Under the Sea. It attacks the Nautilus near the end of the film. The scene with it has since become one of the most famous ones in a Disney film.
There are roughly one-sh*t billion tropes so PLEASE look through them before adding one. Otherwise add what you like. ADDITION: PLEASE read through the trope description provided before submitting something. It's not a huge deal but too often people submit characters that don't fit just because they misinterpreted the title...