The unofficial names describe how the piece moves, while avoiding the problem that the term "champion" already has other meanings in the context of games.
A champion is a person who excels at a game, or a person who champions a cause.
A bouncer is adept at close range confrontation. Bouncers are considerably stronger when they work in pairs.
A jackalope jumps so high that it has no trouble jumping over kings and queens.
Leapfrogs hop over one another.
Nunchucks are dangerous and highly multi-directional in pairs.
Wonder Twins are known for the increase in power they gain from working together.