Tezcatlipoca/Tiamat
A. They're chaos gods, and feel kind of drawn to each other. A lot of drinking goes down, as well as complaining about humans, and they hook up. But apparently they didn't think past that, because Tiamat ends up pregnant. She feels just maternal enough towards it not to get rid of it, but not enough to raise it, and gods know Tezcat isn't really father material. So the baby boy gets given up for adoption.
B. His adoptive family ends up calling him Alastair
C. 1. He ends up inheriting an excellent poker face from his birth parents, which his family figures out pretty quickly means that something bad is coming.
2. He acts on impulse throughout his entire life, especially if he thinks it'll get a rise out of someone. It doesn't make him very many friends, but he can't seem to help himself.
3. And it's his impulsive behavior that gets him killed, when he picks a fight with one of his father's warriors while he's out at a bar one night when he's 28. Tezcatlipoca kills the warrior responsible and eats his heart.