No. The Leviathan is a mystical creature of Hebrew and Christian faith, representing both a demon and a seafaring god. The Kraken is a legend derived from sightings of giant sea monsters, such as the giant squid. Check the links below for detailed descriptions of both the Kraken and Leviathan.
The kraken
The term "Kraken" does not appear in the Bible. However, some scholars believe that the Kraken, a legendary sea monster from folklore, may be loosely associated with creatures described in biblical texts such as the "Leviathan" in Job 41 or Isaiah 27:1, which depict a powerful sea creature. These descriptions often symbolize chaos and the untamable aspects of nature. Nonetheless, the Kraken itself is not a biblical figure.
A Behemoth is a land animal. The Leviathan is a sea creature. Therefore the Leviathan has the possibility of being the largest.
As the kraken is a legendary creature out of lore, it can be argued that no one knows, as no one has studied it.
As the Kraken is a legendary creature, and some doubt it has ever existed at all, it's almost impossible to know.
The Kraken
The Leviathan is a mythological sea creature mentioned in various religious texts and folklore. There is no scientific evidence to suggest that a real-life Leviathan exists. It is believed to be a symbolic representation of chaos or a powerful force rather than a literal creature.
It is a mythical creature, so no, it is not dangerous in real life.
Depictions of the kraken show a giant tentacled monster that is clearly some sort of cephalopod (octopus, squid, or cuttlefish). The closest creature to this known to science is the giant squid.
The Kraken
The Kraken
Well a Kraken is a mythological creature, so there never was a first sighting of something that didn't exist. But it was seen in Pirate's of the Caribbean ;)