A long ass and somewhat all-over-the-place thought piece on the dynamics of character interactions. 
Something I have taken notice to is that I commonly subscribe to Character Contrast Pairings, which isn’t about putting characters into romantic relationships but pairing them up closely with characters having opposite traits. In fiction this is called a Foil (a character who contrasts with another character in order to highlight particular qualities of the other character). However, in fiction a foil usually deals with several contrasting elements, from appearance to personality. But I’ve broken down a subset of different contrasting qualities. This is by no means a complete list, but a list of conflicting qualities that I either find common or have made personal use of. I also do not claim to be the “creator” of these qualities but am simply compiling them and adding on my own thoughts. You’ll find there’s some overlap of qualities as certain character qualities tend to go together.
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Loud Personality- A character who immediately steals focus in a scene. Their dialog and expressions are usually the most distinct and they will usually be the one talking without being prompted to. Their personality dominates others; this is not to say that they have a dominant personality but that they tend to get the most attention on screen.
Quiet Personality- A character who does not talk as much and whose personality is usually more flat. They help balance a scene and provide a sort of ‘cushion’ for louder personalities.
Actionary- Characters who cause actions to happen. They are decision makers and drive the plot forward.
Reactionary- Characters who react to actions and events happening around them. They follow along with the decisions of others and provide feedback, input, and emotional response which can drive character development, but generally not plot development.
Emotional- Characters who are openly emotional and expressive; they are easy to read and usually are meant to trigger more emotional reactions from the reader (empathy, sorrow, anger, humor, etc).
Reserved - Characters with less emotional or expressive responses which help to provide a check for more emotional characters. Meant to be more ‘realistic’ and level.
Static- Characters who experience little if any change in motivation or personality over the course of the story. From start to finish, they are mostly the same character.
Dynamic- Characters that change drastically in terms of motivation or personality over the course of the story. From start to finish, they are not the same character.
Round/Complex- A character with multiple or conflicting motivations that feels fleshed out. They have a broad emotional range and complex personalities.
Flat/Simple- Characters that are “one note” and simplistic. They often express one singular motivation, personality trait, and may have a limited emotional range. These characters can feel like “cardboard” when done poorly, but serve a purpose in giving more time and space for their counterparts to develop when done correctly. In the past, these were usually what “traditional villains” fit into, but this can be ascribed to “good characters” as well.
Positive- Characters who are optimistic and outwardly friendly, even if their intentions are antagonistic. They have a tendency to bring “energy” to the scene, but this is not always the case.
Negative- Characters who are pessimistic and outwardly negative, even if they are considered “the good guys”. They tend to bring a bitterness or ominous feeling to a scene, but this is not always the case.
Expansive Range: Characters who cover the broad emotional spectrum.
Limited Range: Characters who tend to predominately have one “emotion” or emotional range. For example, a character eho may only be seen to express anger, bitterness, or disgust.
In The Know- A character who is aware of the situation and plot on a much broader and more in depth scale than other characters. They hold information that other important characters or the audience might not be aware of. This trait tends to be antagonistic but can provide conflict when both in and out of the know characters are allies/friends.
Out of the Know- Characters who do not know vital information regarding the plot or motivations of others. Something is being withheld from them, sometimes intentionally by others. The trait tends to be primarily for protagonist and main cast characters, but can also be applied to the audience itself in the case of the unreliable narrator.
You might think if character dynamics solely comes down to making characters exact opposites, that repetition would be common. However, because there are so many conflicting qualities, more than I can even mention, it does provide for an expansive combination. Additionally, within larger casts of characters you can have multiple sets of conflicting duos. So you might have a primary cast of six important characters, and within that cast you’ll have different contrasting pairs.
If you feel like analyzing your own cast of characters, use the meme below. Adapt and modify as needed!
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Additionally, there are a few dynamics specific to characters casts I felt like discussing briefly as well.
The Three Primaries: Anger/Red, Joy/Yellow, and Sadness/Blue
-A set of three characters embodying the three “primary” emotions, often (but not always) corresponding to the three primary colors. The emotions at play can have some variation, like swapping out regret with sadness or fear with joy, but the idea is largely the same. The characters stay confined to a limited emotional range, unless the purpose of the narrative is to show them becoming three dimensional or swapping their emotional roles.
The Four Humours
-The four humours refer to the idea of medicine that the human body was composed of four primary fluids that also are related to emotion. There’s a lot more to it than that but essentially this is a four-cast expansion on the Three Emotions above. It also teds I’m going to save some time and quote from TVtropes for this one.
Sanguine (blood): Enthusiastic and full of energy/emotion; the color red.
Choleric (yellow bile): Snappy, irritable, and unfriendly; the color yellow.
Melancholic (black bile): Quiet intelligence and sometimes sadness; the color black.
Phlegmatic (phlegm): Calm, detatched, and emotionless; the color green.
Id, Ego, and Super Ego
-Based on Freud’s model, a three character set up wherein characters take on one part of a “complete psyche”. Id is instinctual and often self-centered, acting without thinking. The super-ego is analytical and tries to provide a sense of moral, acting like a ‘super hero’ that needs to enforce internal/external justice. Ego is the rational in between that has to bring the desires of the Id and the morals of the Super-Ego into balance.
Character Casts
Within a cast of characters, you also have a breakdown of character importance. The more down the line you go, the more “reserved”, simple, and limited they become. This is important in a narrative in order to give time and focus to more important characters. Characters can sometimes move around between casts as the story develops.
A Cast: Reserved for primary protagonists; usually 1-3.
B Cast: Your main cast of characters excluding your protagonists.
C Cast: Supporting roles; they serve a functional purpose but are not as fleshed out or focused on as A or B groups.
D Cast: Re-occurring characters that serve as supporting characters to C Cast.
F Cast: At this point not even really “characters”, but people to fill a scene.
