Who says, "Let him be Caesar"? What light does this throw on the speaker?

The third citizen says "Let him be Caesar" after Brutus has finished his speech justifying Caesar’s killing. Brutus in his speech proclaims that the public can kill him if he too becomes ambitious like Caesar. He has the same dagger for himself and he is willing to lay down his life for his country. The citizens are fully satisfied. They praise Brutus and show their sympathy for the act.