The mother of all cephalopods, Kraken were reportedly the bane of sailors from the middle ages and onwards. Carl von Linné (the guy who invented the taxonomic system) even included it in his first edition of Systema Naturae under the Latin name Microcosmus.
Nowadays, it’s a staple for fantasy worlds everywhere. Kraken has even gotten as far as the 41:st millennium – both figuratively as the hivefleet, and literally as the sea-monsters inhabiting the Space Wolf homeworld of Fenris.
Bonus link: Cephalopod sizes.