Unseater

Messiah is a debatable word, but an element in it has always been that of political leader, unseater of the powers that be.

Source: wiktionary

He was a natural-born unseater of kings, and a throne to him, as a Territorian, was useful only as kindling.

Source: wiktionary

Ordinary form but a most eventful race in which the picture changed dramatically near the finish. The unseaters are rated as having finished first and second with the first three close to previous form, but the fourth home may be the best long-term proposition.

Source: wiktionary

Emmerson Mnangagwa, who went from being [Robert] Mugabe's right-hand man to his unseater, has taken the reins.

Source: wiktionary