Ryder Marína

When the apocalypse started, he had a group of five he was the leader of. Unfortunately, he and one of the group's members, Travis, had a falling out and caused Travis and two others to leave the group. This only left Ryder and Alex. 

Right after the group fell apart, Ryder found a german shepherd and the two bonded immediately. He named it Rex, and Rex protected the two fiercely along with Ryder. 

After coming home from collecting firewood, the trio stumbled upon a kid in their house, stealing from their cabinets, who turned out to be Zack. 

Alex allowed Zack to join them, much to Ryder's dismay. He never ended up trusting Zack, and sometimes even made it very obvious. 

When Alex died, Zack and Ryder split up immediately, taking Rex with him, of course.