I have this theory that there is something going on in terms of character archetypes in stories. We see five of them over and over again: Protagonist, Nemesis, Attractor, Mentor, Trickster.
The Protagonist represents a forward-moving dynamic, a character or characters most often driven by a conscious goal.
The Nemesis represents an oppositional dynamic, a character or characters pushing back against the Protagonist. Typically, this is the source of the story's central conflict.
The Attractor is a character most associated with the Protagonist's emotional life, someone or something connected to their heart.
The Mentor is a character most associated with the Protagonist's intellectual life, someone or something connected to their mind.
The Trickster is a shapeshifter, switching from a Protagonist's ally to enemy... enemy to ally. They pursue their own ego-needs. If that aligns with the Protagonist's goal. great. If not, so be it.
Here is my take of the key characters in The Mitchells vs. the Machines.
Protagonist: Rick Mitchell. Although the story is framed through Katie's perspective (exemplified by her voice-over narration in The Opening) ... and we can certainly look at the story through her perspective as a Protagonist figure, I am inclined to thihnk of Rick as the Primary Protagonist if only because he goes through the most significant character arc. Whereas Katie's psychological journey is reconnecting with feelings she already has about her father, Rick has to develop a new perspective about Katie ... who she is ... what she's capable of ... seeing her as an adult ... and reimagining himself and his role as a father given Katie's transition into adulthood.
Nemesis: PAL. The leader of the Robots with a goal of destroying or subjugating all of humanity. This puts the Mitchells in life-or-death jeopardy.
Attractor: Looking at the story through Rick's eyes as the Protagonist, while he is attached to all of his family, Rick is most emphatically connected to Katie in terms of his emotional life. His feelings toward her have to evolve and mature, as he must be able to redefine his role as Father to his now adult daughter.
Mentor: Okay, bear with me as this may feel likes this take comes out of left field. While there are several moments in the script where a character don a mentor "mask" in providing insights to Rick, including some of the videos Katie has created which allows Rick to see things in a new light), I'm going to lobby for none other than Monchi as a key Mentor figure. Yes, the lazy-eyed dog.
First off, Monchi's dog "wisdom" so confuses the robots, in attempting to figure out who and what Monchi is ("Pig? Dog? Pig? Loaf of bread. System Error!"), Monchi provides the key for Katie to plow through the sea of Robots with Monchi strapped to the front of the car. Indeed, Monchi provides the key moment in the Final Struggle which saves the day:
Pal then JAUNTILY bounces off an AWNING! She's saved and cackling! Aaron sees she's flying towards Monchi!
AARON
Monchi, catch!
HEROIC MUSIC STARTS! Monchi looks up! This is his moment! He STRAIGHTENS one eye ball- then STRAINS and FOCUSES THE OTHER!
PAL
(Scared) Huh?
It's happening! Monchi LEAPS UP HEROICALLY- finally about to catch something for once in his life in GLORIOUS SLOW MOTION!
BUT- it BOUNCES off his face in the STUPIDEST WAY POSSIBLE!
PAL (CONT'D)
Hahahaha, you idiots.
And lands in... a glass of water. Pal's cracked at this
point and the water seeps into the crack.
And the death of Pal. But here's the main thing as far as Rick is concerned: Monchi has trouble seeing the world "correctly" due to the dog's flawed vision (lazy eye). So, too, Rick, who has trouble seeing Katie "correctly" (as an adult who has talent and has to leave home). In effect, the dog is a metaphor for Rick's problem. They share the same flaw. The fact that Monchi can prevail despite of that flaw is a lesson to Rick that can prevail as well.
Trickster: The Poseys feel like Tricksters who for much of the story function as "enemies" in their perfect family lifestyle, but by the end embrace Rick and his family. But perhaps even more significant Tricksters are Eric and DeborahBot 5000, robots who become allies and provide key assistance for the Mitchells vs. Pal and the Robot army.
A reminder: Character archetypes are best seen as tools, not rules. Use them to identify the core narrative function of characters, then immerse yourself in the lives of those characters to identify their unique individual self.