Useful tools and resources that I have found helpful when creating a character, there are many dynamics to a good unique character and if you take in all aspects of developing them you may find that not only are they appealing and fun to you, but to your audience as well. It is important to take into consideration your audience/readers/fellow players.
Photographs can be the best place to start when first visualizing your character. Don't stop at just one, blend a few - take what you like about each of them and piece together a character. That's not to say just put the best of everything together, flaws make characters special too. No one
likes a mary sue (a perfect character, a cookie cut). Add some spice to their looks, scars, deformities, unique colors. However you want to keep in mind realism and fantasy, knowing what would be acceptable for realism and obviously most anything goes for fantasy. Going overboard can make it hard for your audience to visualize them. Of course there is always photoshop. However your pieces will be written, and it's important for the character to be easily visualized (even with their uniqueness) in the mind while reading.
Creating a character persona can be tough, how can you create a believable character? By not going outside of their 'personality' unless your plot reasonable calls for it. Some of the best writers are familiar with what is called the tone scale. Provided you have read and can understand the text, it is the staple for maintaining a realistic believable character in any situation. Using the sliding tone scale also referred to as 'volume' you can easily find what level of personality change to certain circumstances and situations that would be not only believable for the reader, but also retain their interest in your written piece. The only time this will fail you, is when you fail to use it. (Although I promote the tone scale to use for writing and character development, I personally do not affiliate or promote Scientology.) It's rather lengthy, however it is a book. Read How To Chose Your People, By Ruth Minshull