Doubter (noun)

A person who has doubts; someone who is uncertain.

Origin:

Late middle english: from old french doutour, from douter "to doubt".

Examples:

1. He was a doubter and always had to see the evidence before believing.
2. She was a doubter and never took anything at face value.
3. He was a doubter and had to question everything.
4. She was a doubter and needed proof before making a decision.
5. He was a doubter and never took things for granted.