Let me put it simply what I think right now.
Your character will have a role, determined by the kind of situations you want to write about. You want a protagonist who overcomes great obstacles, your role is The Hero
. Others will be the Funny Sidekick, or the Lovable Jerk, things like that.
At this point, you still have nothing in the way of character
What you've got is a role. What many people don't realize that a lot of people could be filling the same role. A lot of people fill the role with their own selves automatically, but that's not a character.
What gives a character substance, or personality? Life experience. There's no way around it. TV Tropes
may help you with the literary role, but nothing short of being able to tell how someone acts and thinks
through your own experience will enable you to write a believable character.
Characters are OK to be two dimensional actually. Some stories are all about that.
And some stories can be managed by just writing yourself and using your imagination too, though not the more advanced ones.
But, if you want to write a good story, that's what you need to do: go! get to know as many people as possible, and get into as many situations yourself as possible! and then
when you are full of your own experiences and stories that you just want to tell is when you can actually sit down and think about whether you should use a literary agent to tell these rather than doing an autobiography.
This of course, only if you are aiming for an Original Character with big O.C. There's nothing wrong with writing archetypes actually.