Who is the only person to have won two unshared Nobel Prizes?

The only person to have won two unshared Nobel Prizes is Marie Curie.

She won the Nobel Prize in Physics in 1903, shared with her husband Pierre Curie and Henri Becquerel, for their research on radioactivity. She then won the Nobel Prize in Chemistry in 1911, this time solely, for her discovery of the elements radium and polonium.