One of the fundamentals of singing is to understand that each one of us does have a unique voice that is more able to be unique as vocal muscular function improves.
This unique vocal quality is determined by the following factors:
The first is the actual construction or shape of our physical bodies such as the spaces in our neck and head.
The second is our mind. How we think and are able to use our imaginations to create sounds.
The third is our emotions. How we are able to access and express our feelings in our sounds without disturbing function. For example, it is very hard to cry and sing at the same time.
The fourth is our basic temperament. For example, whether we are a more excited person or laid back person which would mean that we would naturally infuse our voice with more energy if excited or less energy if laid back.