Emperor Lizong of Song

A distant clansman raised to the throne by a chancellor, and for the first decade a figurehead. He made Neo-Confucianism the official interpretation of the classics — the single most consequential intellectual decision of the dynasty — then joined the Mongols to destroy the Jin in 1234 and spent the next thirty years being invaded by them.

The Song held out longer against the Mongols than anyone else in Eurasia, but the frontier war of his reign is what wore it down.

His empress, Xie Daoqing, was chosen for the throne rather than for him, and as grand dowager she was the one who finally surrendered the dynasty in 1276.