Fans witnessed what happened to Mo’s biological parents, Rachel (Brigitte Kali Canales) and Isaac (Michael Abbott Jr.), in Season 6. In the sixth-season premiere, “The End Is the Beginning,” Isaac, who served as corpsman with the Marines, helps Morgan fend off a bounty hunter. But by the time Rachel, Isaac’s wife, gives birth, Isaac has bitten by a walker. Before he turns — and before Rachel has to put him down — Isaac suggests that they name their baby Morgan after his new friend.

Rachel, meanwhile, survives until the Season 6 finale, “The Beginning,” when a pickup truck wheel crushes her leg as she tries to change a tire. She tries improvising a splint so that she can walk herself and her baby to safety, but it doesn’t work. So she puts baby Mo in a backpack, ties herself to Rufus, her dog, and tells Rufus to find other people to raise Mo, gags herself to protect her daughter and her dog, and then fatally stabs herself in the gut.

And later, Morgan and Grace see Rufus leading a reanimated Rachel toward them. Morgan stabs the walker version of Rachel in the head, killing her for good. And then he and Grace hear the baby’s cries from Rachel’s backpack and rescue Mo.