These two un-cuddly creatures present a classic case for the need to read the text. If you read the history of how B and L have been treated in mythology, in prophetic speculation, and in western literature in general, there would be no way to decide what they represent in Job.
We prefer to read the text, knowing that there is some unknown external history, but also seeing what Job does with the critters.
There are two beasts that follow the previous speech where a number of wild animals are mentioned. So it could be that these are merely poetic descriptions of existing creatures such as the hippo and the crocodile.
Yet there is something more imposing about them, and they are treated separately and more extensively. Why should these two beasts get special treatment. Could they be symbolic or mythic?
Or is it a description of dinosaurs?
The text starts with Job 40:7-14, which raises the questions whether Job is able to bring down the mighty – so that he has the ability also to seek an answer from God. The beasts seem to be illustrations of the Lord’s power to overcome what man can not overcome.
Then again, we have records of the ancients hunting hippos and alligators.
We, for now, tend to think that the two beasts are the hippo and the crocodile, kicked up a notch poetically, so that they can also represent the power of evil. Behemoth, a bulk that can not be withstood, and Leviathan, with armor and twisting coils that envelop.
Is his sneezing fire or the mist he blows out caught in the sunlight? Is that smoke or just hot breath blowing from his nostrils? (41:18 ff.) Either way, he is unassailable to us, but a mere creature to the Almighty.
Leviathan was previously mentioned in Job’s first speech (3:8). So we come full circle in this answer.
The first speech by the Lord (Ch 38-39) show the extensive knowledge of the Lord. The second seems to show his power -even over unconquerable force.