Mortimer "Morty" Smith Sr. ist einer der beiden Hauptprotagonisten von Rick and Morty. Er ist der Enkel von Rick Sanchez und muss diesen oft auf dessen Abenteuern begleiten. Zusammen mit seiner Schwester Summer besucht Morty die Harry Herpson High School.
Morty ist ein Teenager mit kurzen braunen Haaren. Anders als bei anderen menschlichen Charakteren ist sein Kopf kreisförmig und nicht oval. Morty trägt ein gelbes Shirt, blaue Jeans-Hosen und weiße Schuhe wie auch weiße Socken die man nicht oft aber manchmal sieht.
Morty ist ein 14-jähriger, gutmütiger, leicht beeinflussbarer Junge, der Schwierigkeiten in der Schule hat und stottert. Trotz seines geringeren Intellekts hat er sich als guter Zuhörer und Helfer für Rick herausgestellt. Er hat romantische Gefühle für seine Mitschülerin Jessica.
Morty ist manchmal etwas feige, hat sich aber auch schon für gefährliche Rettungsmissionen wie in Anatomie-Park bereiterklärt.Morty ist auch sehr verantwortlich für sein Alter und weigert sich in der Episode "Morty Junior", sein Alien-Hybrid-Kind von Rick töten zu lassen.
Obwohl er sich Ricks Anweisungen oft fügt, hat Morty sich in der Episode "Der fantastische Mr. Meeseeks" gegen Rick durchgesetzt und die beiden in ein eigenes Abenteuer geführt.
In der Episode "Rick Potion No. 9" müssen Morty und Rick ihre Dimension C-137 nach einem missglückten Einsatz eines Liebestrankes und dessen Gegenmitteln verlassen. Sie reisen in eine Dimension in der Rick die Katastrophe abwenden konnte, aber Rick und Morty beide am nächsten Tag bei einem Laborunfall sterben. Rick und Morty begraben ihre Doppelgänger; Morty traumatisiert dies sichtlich.
Rick is Morty's maternal grandfather; he and Morty have a close relationship overall. They come across more as best friends than grandson and grandfather, with Morty addressing Rick on a first-name basis and only adding the grandpa out of gratitude, respect or when he wants something from him. According to Beth, Morty doesn't have any friends, implying that Rick may be Morty's only friend. This could be a reason as to why Morty puts up with Rick's selfish and exploitative behavior.
Morty at first had a very one-sided relationship with Rick, helping him out despite usually ending up in harm's way or nearly killed. However, Morty does have his limits, as he will stand up to Rick when he is pushed over the edge - for example, when both of his legs are broken in "School of Rick", or when Rick destroys the human race in "Rick Potion No. 9". Rick will help Morty out if it is beneficial to him, as in "Der Rasenmäher-Hund" in which he tricks Mr. Goldenfold into giving Morty A's in math so that Morty can help him more on his adventures. However, it is implied that Rick does indeed love Morty, as shown in "Ein Rick kommt selten allein", when Rick starts crying at his memories of Morty, but generally he refrains from expressing it so that Morty does not become, as he puts it, "cocky".
In "Die Monster-Party", after Rick and Summer both throw parties at the same time and trash their house, Morty is presented with an opportunity to stop going on adventures with Rick. Morty claims that he shouldn't care that he wouldn't be able to travel with Rick anymore, but still decides to have Rick fix everything, instead of leaving him passed out on the couch, implying that while Rick's actions do affect him, he would rather continue having adventures as opposed to not having them.
Morty thinks that Rick is "petty", and resents the fact that Rick has trouble "rolling with the punches" when put into a situation he isn't comfortable with; something that Morty does on a near-daily basis. Morty also seems to take what Rick says about him very seriously, as he becomes teary-eyed when Rick calls Morty "as dumb as he (Rick) is smart" in "Ein Rick kommt selten allein". He is also very upset and angered at the idea that Mortys only exist to be human cloaking devices for Ricks, and resents the fact that Rick could just replace his Morty at any time with another Morty from a different reality. Despite all this, Rick still believes that Morty is "the Morty-est Morty", since he views himself as "the Rick-est Rick".
While in the School of Rick, Morty and Summer's relationship is that of a normal younger brother and older sister, they eventually became somewhat closer. It is shown that Morty loves and respects his sister, which is most evident in "Rixty Minutes", where Morty reveals to her he isn't her "real" brother and convinces her to not move out.
Although she seems to envy the adventures Rick and Morty have, Summer seems to hold this more against her grandfather than Morty himself. Morty is also sickened by the sight of a dream version of Summer dressed in sexual clothing in "Der Rasenmäher-Hund".
Morty has a loving but strained relationship with his father due in large part to the frequent misadventures Morty has with Rick. Because Rick often puts Morty in dangerous situations, Jerry is against his son being involved with him.
Morty still goes to Jerry for advice, such as when he needed romantic advice in "Rick Potion No. 9", and agrees to work on his science project with him (though only because Beth mentions that Jerry is insecure with his intelligence). In many ways, their relationship is somewhat reversed: Morty often acts like the mature one, pointing out that he could be masturbating in his room and sparing Jerry's feelings about Pluto not being a planet in "Something Ricked This Way Comes", whereas Jerry often acts like a child, having fits of rage over simple things like golfing and proving that Pluto is a planet.
Morty respects and loves his mother very much, despite the fact that they have yet to have any meaningful interactions with each other. It is implied that Morty respects her more than his father, though he does not think that her method of parenting is very good in "Morty Junior".
Snuffles was Morty's dog, first shown in "Der Rasenmäher-Hund". Morty always treated Snuffles, aka Snowball, with kindness, so Snuffles lets him keep his testicles and live by his side. Morty seems to support Snuffles' decision to colonize a new planet with the other intelligent dogs.
Morty's Gazorpian son born from an alien sex robot that Rick purchased for Morty in "Morty Junior". Morty had a love-hate relationship with Morty Jr. Morty wanted to keep his son safe and happy, as a result, he imprisoned him within their home for his own good, as well as for the safety of the world, due to his son's desire to murder everyone he saw, and wanting to conquer the planet. When Rick tried to kill Morty Jr., Morty intervened, going so far as to risk his own life to save his son's. In the end, however, Morty Jr. became spiteful of his father, going so far as to title his autobiography "My Horrible Father". Morty was shocked and hurt at this, but only said dejectedly "I hope he's eating enough", showing he wanted his son to love him.
- Morty's voice, and general appearance stemmed from an early Justin Roiland short entitled The Real Animated Adventures of Doc and Mharti, which was a parody of Back to the Future. Morty parodies Marty McFly from Back to the Future.
- Another character named Marty with an appearance and voice completely identical to Morty's also appears in Justin Roiland's short Paloni Pitch Presentation. Another identical character named Pumpkinseeds and Peanuts, voiced by Andy Dick, appears in another short; The Unmarketables.
- He was deemed the "one true Morty" by the imprisoned Mortys in "Ein Rick kommt selten allein".
- Morty considers himself to be the "Morty-est" Morty.
- Due to raising Morty Jr. in Morty Junior, this makes him Morty Smith, Sr.