who were the main characters in it?
Rick Sanchez and Morty Smith
Introduction
Rick Sanchez 
the last episode of rick and morty season 3 The third season of "Rick and Morty", an American animated television series
Jerry, Beth, Rick, Morty and Summer. Rick, Morty, Summer, Beth and Jerry are the major characters. Jerry and Beth, Summer and Morty,  Rick Sanchez
Rick and Morty (season 3) Rick and Morty Rick and Morty
Introduction Premise and main characters Premise and main characters
When Jerry asks Beth to choose between him and Rick, the strength of their marriage is tested. Jerry is confronted with the loss of his family, while Beth begins to discover her independence again. Morty and Summer deal with their parents' separation by seeking more control over their lives. The show revolves around the adventures of the members of the Smith household, which consists of parents Jerry and Beth, their children Summer and Morty, and Beth's father, Rick Sanchez, who lives with them as a guest.  The show revolves around the adventures of the members of the Smith household, which consists of parents Jerry and Beth, their children Summer and Morty, and Beth's father, Rick Sanchez, who lives with them as a guest. According to Justin Roiland, the family lives outside of Seattle, Washington. The adventures of "Rick and Morty", however, take place across an infinite number of realities, with the characters travelling to other planets and dimensions through portals and Rick's flying car.
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Rick and Morty [SEP] Introduction
Rick and Morty is an American adult animated science fiction sitcom created by Justin Roiland and Dan Harmon for Cartoon Network's late-night programming block Adult Swim. The series follows the misadventures of cynical mad scientist Rick Sanchez and his good-hearted but fretful grandson Morty Smith, who split their time between domestic life and interdimensional adventures. Roiland voices the eponymous characters, with Chris Parnell, Spencer Grammer and Sarah Chalke voicing the rest of Rick and Morty's family. The series originated from an animated short parody film of "Back to the Future", created by Roiland for Channel 101, a short film festival co-founded by Harmon.