The most important part of any character is understanding how this person views the world. Once you can understand how this person sees the world, it's easier to figure out how they would react to any given situation. For side characters and the like, you can honestly just stop here. If a character only exists for a single chapter, they don't need to be very deep, and having a base understanding of how they view the world is usually enough.   But of course, for main characters, you want to dive deeper, and the next step is to figure out *why* they think that way. What kind of past did they have to make them develop the mindset. Sometimes, it's a single inciting incident that warped the way they see the world--and if that's the case, it can also help to define how they viewed the world before the incident as well. In other cases, there was no single incident that made them the way they are, they just sort of grew up that way. Finally, once you have where the character is right now firmly established, think about where they're supposed to go. What is their arc? Is the mindset they have a good one, or a bad one, and likewise is the arc they're going to undergo a positive change, or a negative one? What kind of events can take them from where they are now to where they're supposed to go, and how does their internal logic shift to get them from point A to point B? Then, once you have all that, you get to add in the final core puzzle piece; other people! With very few exceptions, no character exists in a vacuum. They exist in a world full of other people, and those people affect the way they see the world, and themselves. Everyone operates under their own internal logic that makes sense to them, but the logic they operate by isn't necessarily going to mesh with the logic someone else operates by, and when these two opposing ideologies collide, it's going to create a change in both people. Example time! [spoiler]Step 1: Bop is a lazy, grumpy little kitty cat, who kinda hates being around people, but also can't turn his back on someone in need. He'll pull you out of a burning car crash, and then tell you to get lost. The world is kind of just a chore he has to clean up. Step 2: Everyone in Bop's life either betrayed him, was trying to use him, or got killed because of one of the other two. He's almost never had anything meaningful in life to live for, and the one time he did it got ripped away from him. Because of this he has a very jaded worldview. Still, he just has a naturally big heart, and no matter how much life beats him down, he just can't tell his dump empathy to shut the heck up. Step 3: Bop learns to accept people back into his life, and finds a new family over the course of his adventure. He's still a grumpy old man, but now he's a grumpy old man who cares for these dumb kids who roped him into all this nonsense. Step 4: Bop meets Emily & Aifos, and gets forced to go on this big globe-trotting journey with them. As the only actual adult in the group, he naturally becomes the dad of the group, and after taking care of these two numbskulls, he finds himself actually starting to like them. In the end, he winds up taking care of the orphaned [name redacted for spoilers], finally allowing himself to have a family again.[/spoiler] Now, it should go without saying, this is very simplified. Crafting characters is very nuanced, but this is a general guideline on how I do it. Sometimes Steps 1 and 2 are switched.