The main Character will wake up with practically no memories, no name, no age, nothing. Except the one thing he does remember is being a captive, under extremely severe torture. I dont know if you have ever read the book: "Star Wars: Dark Diciple"? Where "Vos" is tortured, sort of like that. Except he has no other memories. It's a revenge story, he wants revenge on the person who tortured him, but can't help but feel there's something else he can't remember he wants revenge for. How Should this Character be developed, or portrayed? Considering the circumstances it's hard to decide on personality traits, he is meant to be a hero, but he doesn't know that, how would he treat others? I personally was thinking in a cold way. But im not so sure. Please Discuss.
It really depends on the tone, and on the more in depth plot of the book. Is the charactere an empty slate because you wanna have him chase his memories? I think some base plotting should stir you towards a desired development. If you have a direction for your story, your character might become a bit more clear, and you can see where you want him to go. Setting up a story structure might reveal some base for the character. Free-writing the first part of the story might help too, maybe the voice you give the character pushes him in a certain direction already, onto which you can build.
I would rethink your plan to start your story with the character waking up. Not that it's never been done or done well, but it's also something that is done a lot by newer or inexperienced writers. It's something that could easy cause agents and publishers to quickly reject your work on this alone. I would give it some thought and see if you can't come up with a better and more original way to open your story. And there are always more than one option when it comes to this. As far as character development, I think the most important part of that is to make sure there is something the character wants. You've got that. You're character wants revenge. I don't think anyone can really tell you how to develop a character much more than in terms of general advice. This is where you need to make some decisions and find out how YOU want to portray this character. One thing that helps me is to think of developing character and plot at the same time. Try not to separate them in the creation process. It really did wonders for my writing.