Why is Okonkwo called the "Roaring Flame" in Things Fall Apart?

Everything about Okonkwo communicated fierceness and passion.  He was called "the Roaring Flame", a "flaming fire".  He was a powerful warrior, and "whenever he was angry and could not get his words out quickly enough, he would use his fists".  He was "tall and huge, and his bushy eyebrows and wide nose gave him a very severe look...when he walked, his heels hardly touched the ground and he seemed to walk on springs, as if he was going to pounce on somebody".  Okonkwo was a formidable presence, not a man to be trifled with (Chapters 17 and 1).

Okonkwo established his fiery reputation at a young age when, as a youth, he defeated the greatest wrestler of the tribe.  His extreme virility hid a deep sense of anger and insecurity, however.  Okonkwo was mortally ashamed of his father, who was the complete opposite of him in temperament and somewhat of an embarrassment to the tribe.  Worse yet, Okonkwo's son Nwoye showed the same perceived lack of manliness as his grandfather, and, in the greatest affront to his father of all, had left behind the ways of his ancestors and converted to the Christian faith.  Okonkwo could not understand how a man such as himself, known as the "Roaring Flame", could have given birth to a son so weak, and in his eyes, effeminate.  He concluded that he was cursed because "living fire begets cold, impotent ash", and resolved that if his male grandchildren should decide to follow Nwoye's steps...(and) abandon their ancestors...while praying to the white man's gods...he, Okonkwo, would wipe them off the face of the earth" (Chapter 17).