Thanks to this article from Slate, I've learnt that there are squids larger than giant squids and they're known as colossal squids. Maybe the kraken was real after all.

Also, sperm whales aren't their only predators; sleeper sharks, which are half the size of colossal squids, target them too.

The giant squid grows up to 12 m (39 feet) in length, though most of this is made up of its two long front tentacles. The colossal squid may grow up to 14
m (46 feet) or more. Sleeper sharks can grow up to 7.3 m (24 feet).

Interestingly, the sharks appear to prey on bigger squid on average than those eaten by sperm whales. Yes, there's a possibility that the sharks are also scavengers (i.e. they eat the carcasses of the larger squids) but who knows?

[/nerd]