Marshal

The marshal (1 (or 10 in the European version)) is the most powerful piece in Stratego, being able to defeat any movable piece, and safely being able to attack 25-34 of your opponent's pieces. The only pieces that can beat the marshal are the spy (and only if it attacks first), a bomb, or the other marshal. It is usually best to keep your marshal somewhere easily accessible, in case you need it.

Strategies
You should generally not reveal your marshal by attacking low-ranking pieces with it, as if one knows where their opponent's marshal is, they can safely send their general anywhere else. Many people place their marshal close behind a lake so that it is easily accessible, while also being not quite so easily revealed, and this is generally the ideal place for a marshal, with the exception of certain strategies.