Galactic Republic
Plagueis is the main character of the "Legends" novel, "", which explains much of his backstory, including his training under Darth Tenebrous, mentorship of Palpatine, and early plans to undermine the Galactic Republic and drive the Jedi Order into ruins. The novel also reveals that Plagueis' public identity was Hego Damsk II, a member of the Intergalactic Banking Clan.