Who is the Supreme Chancellor who becomes Emperor?

The story behind the answer

The Sith Lord Darth Sidious, hiding in plain sight as a Naboo senator, engineers the Naboo crisis to unseat Finis Valorum, wins the Chancellorship, and manipulates the Clone Wars to secure sweeping emergency powers. After executing Order 66 to eradicate the Jedi, he dissolves the Republic and proclaims the Galactic Empire, installing himself as Emperor.

The other options don’t fit this arc: Finis Valorum is the weakened Chancellor ousted at the start of The Phantom Menace; Mon Mothma is a key Rebel leader who later becomes Chancellor of the New Republic; and Bail Organa, Alderaan’s senator and Leia’s adoptive father, co-founds the Rebellion but never rules the Republic.