Honestly, the kraken's kind of a Norse guy, not Greek. It gets mashed up with Greek myth in modern stuff, which is probably where the confusion comes from. The actual 'kraken' is from Scandinavian folklore, those old sailor tales. If you're looking for a big, tentacled sea threat in classical Greek stories, you're more in the realm of Scylla. She's this many-headed, serpent-necked monster from a cliffside cave in the 'Odyssey,' who snatches sailors right off their ship. Not a giant squid exactly, but definitely a maritime nightmare.
That said, there's definitely a cultural blending that happens. You see krakens pop up in modern retellings of Greek stories, or in games like 'God of War' where mythology gets all stirred together. The idea of a colossal cephalopod lurking in the deep taps into a universal fear, so it's easy to graft it onto any ancient seafaring culture. I remember a Percy Jackson book that kind of went there, mixing up monsters. So while it's not canonically Greek, the vibe has definitely crossed over.
The closest true Greek equivalent might actually be the Ketos, a generic sea monster sent by Poseidon. It shows up in the story of Perseus and Andromeda. That thing is usually depicted more like a serpent or a dragon-fish, but it serves the same narrative function: a huge aquatic beast sent to punish and terrorize.