The kraken is a large, squid-like sea monster in Norwegian folklore. Alfred, Lord Tennyson wrote the lyrical poem, The Kraken (1830), quoted here. As a ‘worshipper’ of books, Aziraphale would be sure to recognise the reference.
The Kraken by Alfred, Lord Tennyson
Below the thunders of the upper deep;
Far, far beneath in the abysmal sea,
His antient, dreamless, uninvaded sleep
The Kraken sleepeth: faintest sunlights flee
About his shadowy sides: above him swell
Huge sponges of millennial growth and height;
And far away into the sickly light,
From many a wondrous grot and secret cell
Unnumber'd and enormous polypi
Winnow with giant arms the slumbering green.
There hath he lain for ages and will lie
Battening upon huge seaworms in his sleep,
Until the latter fire shall heat the deep;
Then once by man and angels to be seen,
In roaring he shall rise and on the surface die.