In the beginning, Salem Alenius wasn't suppose to be. Only his sister, Riot was. But then his father, Dionysus got a prophecy from the oracle. So he begged Eileithyia to make who would be his mother, Naima pregnant with him. She agreed to make him an immortal, not a demigod. And so it happened, Naima Alenius, a Swedish model, was pregnant with two children.
Salem was born three months before Riot (It was a rare case where a woman gets pregnant whilest she's already pregnant, or so the mortal doctors thought.) For the first three months of Salem's life, it was pull of peace. Naima was happy with Salem, he barely cried and was for the most part easy to take care of. But now that Salem was born, Dionysus didn't even come by once month anymore. He was gone. Three months after Same was born, Naima Alenius went into labor once again. This time she gave birth to a little girl: Riot Lee Alenius.
Now Naima was a single mother with two newborn. Their father, Dionysus , hasn't been seen since two mother before Salem's birth.
After Riot's birth, they (Naima, Salem, and Riot) were stalked by something that hid in the shadows, something that looked like badly disfigured human. Salem described it as "An old man, the corner cut from there cut to the top of his head, with brain tissue. His nose, the tip cut off. The underneath of his eyes cut out. He never stood up and only had three limbs, his one arm bent weird angle." So, they moved to Lyle, Alaska.
But even there they were stalked by a creature that looked like the burnt corpse of a human. For what happened between then and camp, look at Riot's bio.