The entire history of Morty is exactly the same history as the original Morty Smith. Including all five episodes of the series that took place before the events of the episode Rick Potion #9 except in his dimension, the dimension's version of Rick was a tiny bit more active than the original and so, he had the energy to make an antidote to turn the Cronenbergs back to normal again. He returned home the next day with his version of Rick and he congratulated him, showing his appreciation for his hard work and started to accept him more. They continued to work on his Ionic Defibrillator, and he helped Rick by passing him a screwdriver. This Defibrillator was programmed wrong, and when Rick finished it, the entire thing exploded on him and killed them both. Just then, the Rick and Morty from Dimension C-137 came in and buried the bodies of their alternate-dimension selves in the backyard and lived out the rest of their lives in their respective places.
In the episode Rixty Minutes, Morty (from Dimension C-137) showed Summer the graves where they buried Replacement Dimension Rick and Morty, explaining to her the events of the previous episode and their deaths.
Morty is a young teenage boy. He has short brown hair that's worn straight and neatly combed around his head. Morty's head in round and roughly in the shape of a circle, unlike many other characters in the show with their oval-like heads. He has a yellow shirt and blue pants and white shoes. He has a pronounced stutter (even when calm) and his voice is constantly breaking due to the effects of puberty.
Morty is a young, good-natured, and impressionable boy who can be somewhat easily manipulated. He has been described as 'challenged' and has difficulty in school. He also has a pronounced stutter. Despite his lack of intellect, Morty has shown to be a good listener and follows directions well. These traits make him the perfect sidekick to Rick. He is interested in Jessica, a student in his math class, but is typically horny in general.
Derived of the events of Rick's selfless and helpful act to cure the world of Cronenberg disease, Replacement Morty changed to become more happy and appreciative of Rick's genius intellect and all his hard work with his inventions. He was a much happier and nicer guy who got along with Rick better and had a lot more fun with him and their presence together was a lot more nice and tolerable.