Characters with strong personalities are memorable and fun to write. They elicit potent emotional responses from the reader. They stick in readers minds and sometimes become cult icons. And despite what you may think, they do not have to be likeable.
Here are a handful that come to mind: Pippi Longstocking; Paddington Bear; Dorian Gray; Scarlett O’Hara. Each of these characters pull the reader into the world of the story with their distinct points of view. Their personalities lead them into engaging and unusual situations. Similarly, strong minor characters create conflict and obstacles for the protagonist, and add color to the story as a whole.
Finding inspiration for memorable characters begins with the study of those around us. There are probably difficult, irrational, stubborn and self-defeating people you interact with on a daily basis. Imagine what would happen if you told those people what you really thought. How would they would react if you leaned into the conflict that ensued? How would those around them react in turn? It is surprising how just one person with a difficult personality can influence others to work in unexpected ways to achieve what they want. Especially when things go wrong!
Other memorable characters are so because of their life choices. Think of the people you know (or know of!) who lead interesting and unusual lives. How do they see the world? What drives them? Why don’t they give up? What is their comfort zone? How would they act or react if placed in an unexpected situation? Or a boring situation?
If you are cursed with only functional, grounded, happy people in your life, Ackerman & Puglisi have written some useful books to inspire you. I especially like their thesauruses of positive and negative character traits.