1. The problem is to find the greatest common factor (GCF) of the variable $b$. 2. The GCF is the largest factor that divides two or more terms without leaving a remainder. 3. Since the problem only mentions $b$ without any other terms, the GCF of $b$ alone is simply $b$ itself. 4. Therefore, the greatest common factor of $b$ is $b$. Final answer: $\boxed{b}$