Kernel of Character on Unital Commutative Banach Algebra is Maximal Ideal

Theorem
Let $\struct {A, \norm {\, \cdot \,} }$ be a unital commutative Banach algebra over $\C$.

Let $\phi : A \to \C$ be a character on $A$.

Then $\ker \phi$ is a maximal ideal of $A$.