Oga, Tatsumi

Tatsumi Oga is the main protagonist in the Beelzebub series, first introduced as a strong fighter, beating up some fellow class mates and then making them bow down to him because they had attacked him in his sleep. He was picked to become Beelzebub's parent as he possessed the qualities of the ideal parent for the future Demon Lord: strong, arrogant, and thinks-nothing-of-fellow-man. In addition to the aforementioned attributes, Oga also seems to take pleasure in tormenting others.As the series continues, it should be noted that the trials Oga has faced and the new friends he has gained has altered his personality somewhat. For example, when the Rokkisei called out Ishiyama to meet them on the rooftop, he initially came alone. But later on when Himekawa, Kunieda, and Natsume soon arrived, Oga smiled knowing that they have his back. Though he retains his love for his cruelty.

(Source: Wikipedia)