I'm creating a character called Jack. (See the Story "Jack" in the Fantasy section to find out more.) I have a rough idea of how to flesh him out(bio, motivations etc.), but I need some ideas to make him interesting and unique. Suggestions please!
I always start my character plan with the questions: What is the most important thing in his life? What are his core values? What is the main goal in life that he wants to achieve? Start with the important inner stuff first then go on to the outer stuff like likes/dislikes, small things that make him happy/sad/angry. Background education. Political views. Last of all the very outer layer: Looks - hair colour, eyes, clothes etc. Once you've mapped every detail of your character down to the minutest details like how they eat their food and little daily habits, you will have a good idea how they will act and speak in every situation. Their personality will automatically come across to the reader of your story.
A lot of people like to write out a character to get to know them better. Maybe just shove him into a situation and see how he reacts to certain stimuli. Like experimentation, only with a human being (if Jack is human, that is). At some point, you should be able to flesh him out through that method. OR you could go with what JMTWeedie said and just list out all of his goals, his attributes, his physical appearance, and maybe all the small things in between. I usually do that to help me get to know a character better or maybe learn how to like him/her more. Sorry, when you say unique, do you mean physically or mentally (personality-wise)? If it's for his personality, that takes time and, personally, a lot of the easy stuff has been done before. What I usually do is take an archetype and put my own personal twist to him/her. That could help too!
First of all, I love your avatar Pythonforger (Disturbed is the best band EVER!) As far as unique ideas for a character... Well, that's kind of a loaded/vague question. I'm pretty sure everyone here could spout off countless lists to help you in your quest but it may not fit well in the overall story/world you are trying to create. When I am trying to think of something unique to do (whether it be a character/story element/fight or what have you), I always think about what is popular and then I do the exact opposite. For example, Harry Potter made magic popular again. Well, what if your character, instead of being a magician, just absorbed magic. He lives in a world where magic is praised yet he can't cast a single spell of his own, however, the man is practically impervious to any type of spell in existence and thus our hero with absolutely zero practical fighting capability struggles to find useful ways to utilize his special ability. Of course, there are many other ways to do this, that is just one example I pulled from my near exhausted mental state. If you want someone to bounce ideas off of, shoot me a PM.