To answer this question you neeed to consider how Okonkwo is presented and his actions in the novel. It is clear from the way that he easily loses his temper that he is an easily irritated man who is proud and overbearing. He is certainly tyrannical in a sense in the way that he runs his family and treats his wives and children, especially the way that he treats his son. However, let us also remember that there are positives to his character. In particular, the third chapter, which fills us in on some important background details regarding Okonkwo's father, offers the following comment concerning the many disadvantages that Okonkwo faced thanks to his father:

But in spite of these disadvantages, he had begun even in his father's lifetime to lay the foundations of a prosperous future. It was slow and painful. But he threw himself into it like one possessed. And indeed he was possessed by the fear of his father's contemptible life and shameful death.

Thus, in addition to the negative adjectives that we can suggest to describe Okonkwo's character, we can also propose that Okonkwo is determined, hard-working, industrious and afraid of being judged as not being manly in the way that his father so obviously failed in this area.