Definitions

1. noun

A German surname, or an American surname of German origin.

“Robert Mueller, the former director of the FBI, is a prominent figure in the Mueller investigation.”

2. noun

The head of the Russian Federal Security Service, previously known as the KGB.

“The Mueller was involved in the poisoning of Alexander Litvinenko.”

3. noun

A German term for the head of the Russian Federal Security Service.

“The Mueller was accused of espionage.”