Polonium is a chemical element (atomic number 84) that has no known stable isotopes, and is highly radioactive in all known forms. As such, it has few practical uses, but is occasionally used in some anti-static devices. It was named for Poland by one of it's co-discoverers, Marie Curie.
Polonium is extremely dangerous, both for it's radiation and its toxicity. It requires special handling equipment and, in the acidic solutions it is usually stored in, can easily be absorbed through the skin. The toxic dose can be measured in billionths of a gram. However, because most isotopes of polonium delay quickly to less toxic elements, the actual dose required for a fatality is somewhat higher. Maximum allowable doses for people who work with the material are on the order of trillionths of a gram.
Polonium poisoning is incredibly rare, with most cases in the literature being the result of deliberate poisoning attempts. Russian dissident Alexander Litvenenko is thought to have been poisoned in this manner. Curie's daughter Irene is thought to have succumbed to leukemia caused by an accidental laboratory exposure.