Varies - but traditionally, it would be animals representing leadership, masculinity and dominance, such as bulls, lions, eagles and wolves. Also popular are mythological or legendary beasts, such as dragons and - especially - gryphons.
Highly organised animals also work - ants and bees in particular - but tend to be more of a general symbol for armies than symbols for the army general.
no
me
A dove.
lion
The bird.
the lion
The ox.
The fish.
Lions
The Eagle.
The Vulture
the ram is the animal of aries, it symbolizes as great courage