The Empyrean Commonwealth (typically shortened to simply "The Commonwealth") resides entirely in space and dominates the Barycenter, where all hyperlane traffic passes through. It is the sole merchant republic that builds the largest Titan-class freighters servicing the major tradelanes. They also maintain many waystations and other infrastructure. As the principal gatekeeper of interstellar trade they maintain an outsized influence on international politics.
The political entity most enamored with laissez-faire trade, the Commonwealth holds broad trade relations across The Bary, and more recently have established embassies on every inhabited world. However, the higher leadership apparatus of the Commonwealth is largely a mystery. Heads of state from other nations have only ever met emissaries, or seldomly the mayors of individual stations or outposts.
With no capital to speak of, the next closest thing is the megacity Port Angelice, which is built within a large fragment of relic Terran superstructure.