What makes a character?
The question above could have many answers. One could be their personality. Another could be their backstory, or their quirks, or other important stuff. What do I think makes a character? I believe all the above answers are true, it all hinges on the way you develop your character. You could write an amazing story with a great character who has an intriguing personality and backstory, but if the character isn't well developed... that could be very not good... So make sure to put a lot of time into developing your characters, whether they be the main character or the guy who just happened to be in the wrong place in the wrong time. For an example of one of the characters I am developing, I am going to use Kamryn Scott
Kamryn Scott is 12 years old with brown hair and blue eyes, she has (very) enhanced strength and anger issues. She likes spending time with her friends Caddie and Miranda, any kind of soda, white chocolate, and her brother Korey and his friend Jarrod (when they aren't being idiots). She dislikes coconuts, Korey and Jarrod (when they ARE being idiots), Marcus, the color orange, and stilettos. She has a weird quirk, whenever she gets angry and there is a piano around she will throw the piano (much to the dismay of Jarrod). She has zero tolerance for stupidity, she isn't very nice, and she just doesn't like most guys.
So lets see your character. I chose a supporting character, but you can use whatever character you want.