From the publisher's blurb:
A commander is someone who commands his subordinates (an army or adventuring party). NPC commanders are usually found at the head of an army's unit or units, either on the march or defending a castle at a strategically important site. The PC commander can support his adventuring party at a dungeon with his Formation, Feat Lend, Tactics and Saving Throw Aid abilities. A class is flexibly designed to imitate the abilities of famous historical or fictional officers known from books and movies (Julius Caesar, Genghis Khan, Napoleon Bonaparte, William Wallace from "Braveheart", Maximus from "Gladiator", Theoden from "Lord of the Rings?). A commander has a tactician's mind, a cartographer's overview of disputed landscape, and a way with words that can inspire his subordinates to give their all at war.
Commander prestige class can be found in The Forge "Strongholds 2: Barony" the pdf e-book also. ommander prestige class will be expanded in "Strongholds 3: County" with some battle-system abilities.