The word dragon is translated jackal by most modern versions. Job likens himself to the wild jackals and calls them brothers to indicate his closeness to them.
‘How great a temptation Job endured when it seemed that his praying to God did him no good, for that is our last refuge in all our adversity, and the sovereign remedy that can never fail us. When it seems that we are disappointed in our hope, and that God acts as if he were deaf, and that our prayers profit us nothing, it is as if hell gaped upon us, and we are bound to fall into utter despair if God does not hold us back, and show that his delay in helping us is not without cause … If God now and then suffers us to linger in pain, let us wait patiently and fight against such temptations, yes, and let us endeavour also to obey him. For it is not enough to pray to God, but we must also bridle our affections … Although Job was a mirror of patience, yet he was not so self-controlled that he mastered himself when he spoke of God, for he did not proceed with that reverence that he ought to have had, but ran headlong into this temptation. Although he was not overcome, he only succeeded in resisting with much ado. Seeing that the passions within us are so out of square, let us learn to hold them, as it were, in prison, and when we have fought hard to tame ourselves, let us remember that there is much imperfection in us – enough for God to condemn us if he did not bear with us in his infinite goodness’ (Calvin – in modern English).