The Vancouver aquarium used to keep a number of giant pacific octopi in their back rooms so the could rotate them through the exhibit (the one on public display gets stressed, so they're only on duty for a period before returning to the back tanks). I used to play with the ones in the back, and I can confirm that they are intelligent and have interesting personalities. One of them would always greet me in the same way, by sliding the thin end of its tentacle out and very gently feeling around my fingers while flashing different colours.

They were pretty bored back there, and the aquarium's policy was to return them to the ocean after a few months.

That was genuinely charming.