Field Marshal was a military rank above general.
Thatcher was a UNIT field marshal stationed in Geneva in the 1960s or 1970s. (TV: The Invasion)
Erwin Rommel was a Nazi field marshal during World War II, (COMIC: The Instruments of War) as was Wilhelm Keitel. Keitel was responsible for signing the documents of Germany's surrender to the Soviet Union at the end of the war. (PROSE: Just War, AUDIO: Just War)
Henry Wittington Smythe was a field marshall who stayed in the Carstairs hotel on the planet Chelsea 426. He had fought in many wars, including the Martian Wars, the Battle of Mercutio 14 and the Siege of the Hexion Gates, where he encountered the Sontarans. (PROSE: The Taking of Chelsea 426)