Tatsumi Oga (男鹿 辰巳, Oga Tatsumi) is the main protagonist in the Beelzebub series.
Oga is 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. Oga and Beelzebub cannot be separated by more than 15 meters or else it may result in instant death for Oga, according to Hilda (as of chapter 38, the distance has increased with 8 centimeters). He accidently made a contract with Beelzebub after Hilda wounded his cheek with her weapon at the electric fence.