Puissant

puissant \PWISS-uhnt; PYOO-uh-suhnt; pyoo-ISS-uhnt\, adjective:
Powerful; strong; mighty; as, a puissant prince or empire.

"Randolph's timely intervention in the dispute demonstrated that he was a puissant leader."

There is also a noun, puissance.

"Randolph, the empire builder, exuded puissance."

Poissons are French fish, silly!