Bruno Pontecorvo and the neutrino

This paper commemorates the 100th anniversary of the birth of the great scientist and neutrino researcher Bruno Pontecorvo. His major contributions are reviewed, including the radiochemical method of neutrino detection, the idea of the $\nu-{\mbox e}$ universality of the weak interaction, and the proposal of an accelerator experiment to prove that $\nu_{\mbox e}$ and $\nu_\mu$ are different particles. Pontecorvo's fundamental idea of neutrino masses, mixing, and oscillations is discussed in detail, as is the development of this idea by Pontecorvo and Gribov and Pontecorvo and the author.