Mortimer "Morty" Smith was the grandson of a Rick Sanchez, whom he left after Rick destroyed their world. In their new dimension, Morty became an oppressive dictator with his mother as his helper.
Several years ago, Beth brought Morty and Summer to Dimension 304-X by using their Rick's Portal gun. Their Rick had destroyed their world, so they had to escape him. When they entered their new world, Morty became a scientific genius, but he was obsessed with ridding the multiverse of Ricks.
At some point, he decided to seize power as dictator and never let it go, allowing it to corrupt him and drive him crazy. He created tools to look through realities, but not being able to travel there himself due to the low battery on the portal gun. This meant he had to find someone else who could travel between dimensions, Rick Sanchez from Dimension C-132. Morty set his scientists out to create a monster to kill all Ricks in all dimensions, but this drove him to a fight with Summer and Summer to leave him and Beth.
Morty sets loose the monster created to kill all Ricks in order to draw Rick(C-132) to his dimension by using the last energy in the portal gun. He succeeds in having Rick and Morty from C-132 come to his world, but is told by his mother that they were unsuccessful at capturing them. She later tells him that Summer had taken them to the Resistance base, but Morty corrects her on that she is not his sister. He decides to activate their sleeper-agent (Jerry) to blow up the Resistance base, and sets his mother to do that.
After the Reistance base is blown to a burning pile, he travels to the location to find Rick on the ground. He kicks Rick unconscious to take him back to his own base to search him for his Portal gun. Morty decides to leave with Beth remaining to make Rick talk by any means necessary, but she is unsuccessful. As Morty is starting to mock Rick for not understanding, he is allerted of intruders. Morty orders a complete lockdown of the base, once again leaving Beth with Rick.
He finds Summer and Morty (C-132) in the portal gun-room and attacks them with a Walker. He tries to reason with Summer, saying they both want a world without Rick, but she is too weak to do so. When Summer notes that Morty sounds an awful lot like a Rick, Morty gets infuriated. However, to prove he is nothing like a Rick, he exits the Walker. After accusing Summer of being the reason why is this way, Morty (C-132) tells him how bad stuff just happens and not anyone else's fault. Morty and Summer reconcile, but are then crushed to death by Jerry when he enters with a huge armoured vehicle.