Some people say plot and setting are more important than characterisation because the former shapes the latter anyway. Others say character drives everything. Of course, both capms are correct because it completely depends on what kind of story you are writing.
Is it plot-driven tale of epic proportions with a cast of way too many to pay sufficient attention to or a character-driven oddyssey where the choices and deveolopment of one person drive everything else? It can be both but that, my friends, is incredibly hard to achieve well.
The Empyraeum Cycle started off as a collection of such character-driven story arcs; first person short stories in the the Collections and tales riven predominantly by one character or another (though mainly from a third person perspective) in the the Novellas. The Empyraeum Trilogy of novels is going to be set in third person and will, as you may well have seen, have quite the cast of characters. Of course, there will be some characters who complete their own version of the famous "Hero's Journey" throughout; Sean Ollimur, the mysterious Kat, Gabriel, and some others, together with their vast supporting cast. This is what makes Empyraeum such an ambitious project; it is aiming to be a part of the Space Opera genre, as well as something quite different; combining ancient history, sci-fi, myth, magic. and cyberpunk together with another influence or few. Those that have paid attention to artworks we have released can see many of those influences already.
Character Journey
Of course your character is expected to set out on a journey as part of the story, to leave behing their comfortable life - either willingly or unwillingly - to discover a new one along the way, as well as discovering a thing or two about themselves in the process. This is, of course, something we like to call character development.
As humans in our regular lives, I doubt any of us is exactly the same person we were in our teens. As life progresses and we experience, as well as learn, new things, we see the world differently and, whether we realise it or not, it changes us. I will use a personal example here; when my wife and I met, I had just come out of a period of incomparible difficulty and chaos I had allowed into my life; I was a nervous and insecure person in many ways. Over time I slowed down and, with her pregnancy and the birth of our daughters, my wife claims I underwent an incredible transformation. A positive one, of course, into a steady, calm, and decisive person who was afraid of nothing, at least n the surface. Now she doesn't know I used to be like this decades ago and simply, thanks to her love and support, managed to recover my old self back, with a positive change or two thrown in.
There is a lesson in this; not all change is new. Your character can experience trauma and recover a part of themselves they had thought forever lost. Not all backward motion is bad.
A character must change, though, for a major character that remains changless from their first appearance to their last is a two-dimensional one. This should be avoided unless said character is a Lesson.
A what? A Lesson. Let us say that Main Character is resisting a change they must undertake, a decision they must make, a direction theu must travel in in order to achieve their goal. Two-dimensional character does not change and suffers some mishap - either a permanent or temporary one - and serves a wake-up call to the Main Character; often taking the required step in order to honour the noble sacrifice - or stubborn stupidity - of said character.
A Warning to New Writers
Neither race nor gender defines a character. There is much pressure these days towards inclusivity. One must have a racially, sexually, and community diverse cast in your works. Must one? In my opinion, only if it fits.
In the Chronicles of Enoch, the cast is delightfully diverse because of the worlds it is set in. Ancient Eastern civilisations, lost lands, modern-day Atlanta and Albuquerque, to name just a few. Atlanta, for example, is one of the most ethnically diverse cities I have visited and lived near; East Asians of all kinds, Indians (from India) and Pakistanis, Jamaicans, Latins of all kinds, African Americans of infinite variety...it was impossible not to represent that diversity among my cast there.
In Empyraeum, the core cast, as it were, are more monoethnic; proto-Greeks mostly with a character or two thrown in. However, anyone that has spent any length of time in the London of our world must surely know that the Lùndùn of the Empyraeum is going to be rather similar, especially once it effectively becomes the capital of first the Union and then resistance against the same. It's only to be expected that a taste of London be found in Empyraean Lùndùn.
Now, none of my more 'diverse' characters started out as any particular race of belief. Acora the Kalshodar leader of the Sons of Nemesis just seemed to suit the race he took on in the artworks of him; his developing character seemed to demand it. Paxxi, the nonbinary trans augmented hacker character, just seemed to fit their chosen identity. Commander Soong appeared to develop his own personality and background.
You see, the Empyraeum was founded on the idea of diversity, in its way, because Alexander never tried to impose Greek views of the world upon those nations he conquered. In fact he even adopted Persian and Babylonian customs himself and recruited people from those nations into his army. It stands to reason that he would not change that philosophy as he began to found the Empyraeum. In fact, in deveoloping ESG or Empyraen Standard Greek, we intentionally chose diverse linguistic influences from both extremes of the Empyraeum as some of the dominant ones in order to represent that.
My point? If the colour, ethnicity, sexuality, or gender of a character has nothing to do witrh their role in the story or development thereof, why include it? In many works, some such things are implied but never directly told. Anne Rice's vampires are said to be bisexual but she has never directly said it. In the Chronicles of Enoch, there is talk about Asmodeus and Julian's relationship but, I assure you, I will never go into depth on that because it doesn't affect their story (and what some of your have imagined is quite impossible anyway).
In Empyraeum, Paxxi's identity is mentioned but they go on to be somewhat dismissive of it themselves and assert that it really is not something they think about a lot, people respect it anyway.
The danger for those thinking inclusivity is mandatory is making a character of one archetype or another just to tick a box and creating a potentially harmful stereotype or obvious insert as a result; a character who behaves as they always did and not how someone of their ethnicity, community, or identity would; that there is no reflection of that aspect of their character anywhere in their behaviour or such behaviour is forced and artificial.
That will hurt the cause far more than the lack of such a character might.
Giving them Free Rein
I have often joked about this myself, often at length. That saying we writers have that characters appear to write themselves sometimes. Asmodeus started off as a boss-mobster-monster in the prologue and a single chapter and a half before dying later on as a plot device. Sham was a generic Mentor-to-The-Chosen-One character in the abandoned Trinity series. Both came to dominate their respective series and, I have chuckled, appear to have rebelled against their creator. In actuality, I do so love the trickster type character; the heroic anti-hero type who at times does the wrong things for the right reason; one that will do the things the heroes cannot but which need to be done.
I do enjoy getting inside the head of the complex manipulator who genuinely thinks that he is doing the right thing even though, on occasion, his best plans aft gan aglen! His motivations are always the most interesting and intriguing. Both Sham and Asmodeus as good people, deep down (though you have to dig a lot deeper with Asmodeus), and doing what they think is the only possible way to help those they care about.
The fact is that Sham and Asmodeus are extreme examples of the Free Rein Principle (patent pending) but they are also excellent illustrations of it. Their characters and the story itself needed them and their previously planned roles expanded to fit the need; enhancing the story rather significantly. Let your character be what your story needs them to be, is the lesson in that.
Sham became Indian because it suited him, Asmodeus became ethnically indefinable because that's who he is; a powerfully chameleonic personality.
Let your character be who she, she, it, or they need and 'want' to be; not who you or the nebulous 'they' of the internet think they should be.
Conclusion
As you have seen, characterisation is often the hardest part of the art of writing. Who your character is, what they are, their thoughts and motivations, will actually shape the story around them. At times, they will shape the story and at others, it will shape them. All of our previous episodes and 'lessons' also come into play here because the fabric; the context of your world and your story are important because the 'rules' you have built into it will influence what your character can do and, therefore, how they can change. The influences and crises that will push this change will also be controlled by the environment in which they find themselves.
In short, you must realise that both story, plot, and character may well change one another unexpectedly. A challenging situation one character finds themselves in has multiple ways out of it and you had, previously. chosen route A. However, as your character develops, you realise that this course of action does not suit the character at all; in fact route B doesn't either, only route C does. Route C, however, leads to unexpected developments in the story and some retrospective editing on your part. As annoying as this might be, I think it's more important to be true to the character then to your original outline. right? It makes the story feel more organic and natural as it were.