The three naturally-occurring actinide alpha decay chains given below—thorium, uranium/radium (from U-238), and actinium (from U-235)—each ends with its own specific lead isotope (Pb-208, Pb-206, and Pb-207 respectively).
That would be pollonium 212 because an alpha particle has a mass number of 4 and contains 2 protons. 212 - 4 = 208 and atomic number goes from 84 to 82.
