I don't know if this problem is known or not, so any information would be appreciated:
Let $\cal A$ be an $\Bbb{R}$-algebra of (not necessary continuous) real valued functions defined on a topological space. I would like to know what is the necessary and sufficient condition that $\cal A$ is isomorphic (as a ring) to $C(X)$ for some Tychonoff space $X$.