His backstory starts before he was even born. His mother and father met
in a bar as children, and became quick friends. They grew up, as people do, and eventually left the bar to go live their lives, after his father's band incidentally exploded Earth, as forseen in an ancient prophecy. However, when they left, they wound up in an entirely different reality (and time) from the ones of which they were a part. It was 1991 before Teja was even born.
He is the youngest of four children, and the only son. He was with his mother when they returned to a world not even of his own reality, much less the realities of his parents. She disappeared when he was three, and was taken in by an elder Skwisgaar Skwigelf and his wife, and at seven, he was adopted by the band of that world's healer, Sadako Yamamura. He was raised by her, and taught much by Charles Foster Offdensen, and was raised in Mordhaus.
While his sisters inherited all their mother and father's sweetness and positivity, Teja seems to be the one who inherited his father's rage and anger management issues. He's staunchly serious, and although he does have a kind side to him, it's terribly stifled by the inability to simply be happy.
At the age of 16, he tried dating a klokateer, and that ended in him finding out she was a werewolf when he tried to break up with her. Needless to say, that went pretty badly. He was happy when she got taken out of reality.
After many years of studying, Teja has grown proficient in combat, business skills, assassination, and anti-gnostic necromancy. He's not so great at anything not pertaining to these fields. He is sadomasochistic, and although he enjoys skullfucking the hell out of people who have wronged the band or his family, he has a very strong morality. He is vehement in his alignment of Lawful Evil.
One alternate verse: After many brushes and encounters with Kings of Hell, Teja wound up inheriting the mantle of the King of Wrath. He is not very happy with this situation, having never wanted to become demonic, or lead anything but a somewhat normal life. However, he is slowly getting used to the changes, both physical and metaphysical. He is a competent leader, and although he is technically demonic, his loyalties to his family have not waned. He will continue to protect and care for his family.
Another altverse: Teja has refused to be associate with demons after destroying the demon who had tried to screw him over, and has gone on much the same as he always has.