We do see him briefly in action in Attack of the Clones at the First Battle of Geonosis, and of course we witness his death over Cato Neimoidia during Order 66 at the end of Revenge of the Sith. General Plo Koon appears briefly in all three Star Wars Prequel episodes, usually sitting silently as Obi Wan Kenobi or other members on the Jedi Council talk.
Plo Koon may be the most well-developed of all the Jedi who populate the secondary character list of Star Wars: the Clone Wars, although you’d never guess it from what you see in the three Prequel movies. And there’s perhaps no better personification of this that Jedi Master Plo Koon of the Kel Dor. It rescues this part of Star Wars from the dustbin of history and makes cool what was initially, shall we say, rather lacking. Star Wars: The Clone Wars is the best thing to come out of the Prequel era.
